Let's start with application. Think about exactly what you want out of your headphones including the environment where you will be using them. Is it music, gaming, podcasting, movies or recording? Where will you be using them? At work, outside, office, home and will others be around you or for the most part by yourself.
Open Back VS Closed Back
The decision between open back and closed back headphones can be a difficult choice. Hopefully this article will clear things up a bit and make your decision a little easier. Circumaural basically means around the ear, a technical term you may have read when looking for headphones.
Open Back Headphones
Open back headphones means the back of the ear-cup are open. The speakers are designed to emit sounds towards and away from your ears, through a lot of openings. Because of these openings sound escapes and everyone around you can hear what you are listening to. Outer noises may also mix with your music, game or even when recording. They are designed this way so air can pass through for a more natural sound. Great choice for mixing in the studio. If your surroundings are quiet and for the most part you are by yourself then open back headphones will give a feeling of openness and a fantastic listening experience. Generally the ear-cups do not heat up as fast for those longer sessions.
Closed Back Headphones
Closed back headphones means the back of the ear-cup is closed and there are no openings. The back of the ear-cups are a hard shell. The ear-cups will cover the entire ear and block any sound from escaping. No one will be able to hear what you are listening to and you will not bother anybody around you. They will give you a feeling of being isolated, most say it's an "in your head" experience. You will not hear ambient noises from the outside world and get distracted. Some say poorly designed closed back headphones sound hollow without the feeling of depth. Closed back can also create false low frequencies during a recording session but no external sounds will be picked up by your microphone. They are excellent for closing yourself off to the world, critical listening and not disturbing others.
Semi-Closed Back Headphones
There is one more choice to consider and that is a semi-closed back. Gives you some form of isolation but sound will still leak out. They have holes or slots in the back of the cup, but the cup is partially closed. If it's quiet like a library you will probably not be able to use them. You also may have a harder time finding this style for a specific budget.
Once you have decided on your preference, consider your budget, Brand name, are the cables interchangeable and desired look. Do you want headphones with a mic or a stand alone microphone for even better crystal clear sound?
Hopefully this helped clear up a few questions and will make your decision a little easier. If you have any questions or comments to add to help out someone in their choices, or what preference you prefer feel free to add your information.