The difference between the evil Angels and the good Angels is one of their own choice.

Psalms 104:4  "Who maketh his angels spirits; his ministers a flaming fire"

We know, from Scripture, that God created all of the Angels, and all were originally created in a state of righteousness. Some of the Angels, however, decided to follow Satan when he led a revolt against Heaven. These "fallen Angels" are often called "unclean spirits":

Matthew 10:1  "And when he had called unto him his twelve disciples, he gave them power against unclean spirits, to cast them out, and to heal all manner of sickness and all manner of disease."

Devils, that often encouraged the people to worship them as gods:

Deuteronomy 32:17  "They sacrificed unto devils, not to God; to gods whom they knew not, to new gods that came newly up, whom your fathers feared not."

And by the term "demons". These "demons" or "devils" know and fear God, but not enough to repent of their rebellion:

James 2:19  "Thou believest that there is one God; thou doest well: the devils also believe, and tremble."

A clear sign of instability. To know and fear the Creator, yet to refuse to repent and throw yourself on His mercy is clearly unstable, bordering on insanity. The fact that they "tremble" at the knowledge of God is a clear indication that they are, after all, created beings. They may be different in their creation than we are, but they were created. They are not "gods", nor do they have the power of God.

One of the most outstanding tactics that Satan ever came up with is the concept that evil Angels (I'll refer to them as "demons" from this point on) do not really exist. Since the dawn of man humans have always believed in demons. You can go to the jungles of South America or Africa and find people who, having never heard of Jesus Christ, they have heard of demons - and many people worship them. In human experience there are a number of things that have occurred that we write off as "mental illness" that could well be the work of demon possession or demon oppression. Jeffrey Dahlmer, the mass murderer, killed his victims, then molested or ate their dead bodies. Many of the most gruesome murders have been committed in human history because people "heard voices" telling them to do it. Many of the suicides that occur all around the world could be the result of demon oppression.

The problem is, with the rise of modern medical practices the idea of "demon activity" is ridiculed. After all, demons were just superstitious nonsense of the ancient people. Satan wants you to believe this. When demons become a figment of the imagination, it becomes easier to assume that God, the arch-nemesis of demons, is also a myth. Some have suggested that all of the incidents of demon possession shown in Scripture was merely a type of mental illness, misunderstood because man was so ignorant back in those times. Some have suggested that demons are just the re-incarnated souls of pre-Adamic men, people from a bygone era, or ghosts of the long dead demanding bodies for their corporeal spirits.

Mark 5:7-13  "And cried with a loud voice, and said, What have I to do with thee, Jesus, thou Son of the most high God? I adjure thee by God, that thou torment me not.  For he said unto him, Come out of the man, thou unclean spirit. And he asked him, What is thy name? And he answered, saying, My name is Legion: for we are many.  And he besought him much that he would not send them away out of the country.  Now there was there nigh unto the mountains a great herd of swine feeding.  And all the devils besought him, saying, Send us into the swine, that we may enter into them.  And forthwith Jesus gave them leave."

If demons are only a "figment of the imagination" then we have to ask this question: Who was Jesus talking to? The "figment" spoke loud enough for Mark, who recorded the incident, to record it. This demon, "Legion", was more than just one, but multiple demons that inhabited this man. They showed rationality (they knew who Jesus was), this proving they were not animals but created higher life forms. They expressed a desire, which Jesus satisfied. In short, these demons showed all the volition that a higher created being could show. They were not man, but not animal either. They were demons.

The demons became what they are today, evil, by choosing to follow Satan over God.

Revelation 12:1-5  "And there appeared a great wonder in heaven; a woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars:   And she being with child cried, travailing in birth, and pained to be delivered.   And there appeared another wonder in heaven; and behold a great red dragon, having seven heads and ten horns, and seven crowns upon his heads. And his tail drew the third part of the stars of heaven, and did cast them to the earth: and the dragon stood before the woman which was ready to be delivered, for to devour her child as soon as it was born."

Matthew 25:41  "Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels"

The Bible tells us that a "third part of the stars of the Heaven" followed the Dragon, Satan, in his revolt. They made this decision of their own free will. Because they made this decision, God made the decision to prepare a place of eternal bondage for them, a lake of Fire. This tells us, by inference, that Satan and all the demons will one day reside in bondage of flame.

Demons are spiritual, immaterial, and incorporeal. The Bible drives this point home by calling them "spirits" (Matthew 8.16). They are also intelligent beings (Mark 9.24), as they knew who Jesus Christ was and know that they will go into the abyss (lake of Fire) one day. These beings are also immoral. The Scripture calls them "unclean" (Matthew 10.1; Luke 8.27), sinful beings.

Are Demons more powerful than man? Well, yes and no. Demons are beings of light, and much more powerful than man. However, Jesus Christ gave His disciples power over the Demons:

Luke 10:17-20  "And the seventy returned again with joy, saying, Lord, even the devils are subject unto us through thy name.  And he said unto them, I beheld Satan as lightning fall from heaven.  Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.  Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice, because your names are written in heaven."

As long as they approached the Demons in the power of His name. The Christian in fellowship with God does have power over the demons, but this is BORROWED power from the Son of God. Do not assume that we, who are mere mortals, have power over the demons ourselves. Also, no icon nor chant gives us power over the Demons - only faith in the name of Jesus Christ.

Every army, if it is effective, has a highly organized structure, and Satan's evil army is no exception. Not all of the fallen Angels are free: some of the "third part of Heaven" is free, however, some demons are presently imprisoned in the Abyss:

Revelation 9.1-10  "And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit.  And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit.  And there came out of the smoke locusts upon the earth: and unto them was given power, as the scorpions of the earth have power.  And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads.  And to them it was given that they should not kill them, but that they should be tormented five months: and their torment was as the torment of a scorpion, when he striketh a man.  And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them.  And the shapes of the locusts were like unto horses prepared unto battle; and on their heads were as it were crowns like gold, and their faces were as the faces of men.  And they had hair as the hair of women, and their teeth were as the teeth of lions.  And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle.  And they had tails like unto scorpions, and there were stings in their tails: and their power was to hurt men five months."

...or the bottomless pit. These demons will be released on the earth during the Great Tribulation to torment all those who, in folly, rejected Jesus Christ as Savior. Other demons are imprisoned in Tartarus:

2 Peter 2:4  "For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment"

Jude 1:6  "And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day."

These are the demons who sinned in Genesis 6.1-7, the "Sons of God" who tried to pollute the human race. God had them cast into Tartarus, and they will be held there till the final judgment.

The free demons who inhabit earth exist under Satan, the prince of the Demons (Matthew 12.24; Ephesians 2.2). Satan has lower chiefs that rule demons under him (Daniel 10.10-14):

Ephesians 6:12  "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places."

That are called, by rank, (1) Principalities, (2) Powers, (3) and Rulers of the darkness. Regardless of rank or power, however, the end of the demons and Satan is promised by God. They shall, ultimately, be cast into the Lake of Fire to suffer eternal imprisonment with all those who rejected the power of Almighty God.