Stick to Mw2 man..
Combat Arms is like a shittier version of Mw2.
It's like a generic Mw2 with crappy resemblances and more bugs, etc;.
Think of Mw2 as a modern day computer, it's very customizable, if so, it's fast, strong, and great.
While CA is like the first laptop. shit, crap, fail invention. but then again, it will sprout up new things