This is my favorite style. Rushers are always on the move looking for enemies to kill. If you practice and get good you can get a lot of kills. Odds are in your favor. Also make note that this is likely to give you a lot of deaths too.
B. Snipers
A good sniper is a huge advantage on any team. When you start out, you will more than likely only be able to kill campers and other snipers, its a lot easier to kill a sitting target and it takes a good bit of practice to before you will be able to hit moving targets. On top of that, Also normally your enemies don't die with 1 kill unless your playing hardcore games or a headshot.
C. Melee attackers
I would consider Melee attacking to be type of hybrid playing style. You will see some people are pros at it and could take out a whole team. They're very fast, cant detect them, silent. Aim for their feet and Beware of the ninja.
D. Campers
I don't think anybody likes campers not even other campers. Why? Campers try and find a high traffic area and stay there. They try and make kills as easy as possible. They are a real pain in the team games.
Make sure to give every style a good chance, to find the best style that fits best and works for you. Except if it's camping. If you do, please just don't play. Ever.