Well, I've personally tried Crossfire and you're right, it's incredibly harder to get kills on it. In fact, I attempted to play it, and I was unable to get a single kill. For that reason alone, I personally enjoy MAT much more. Additionally, I believe it just has a better general feel to it. However, if you're talking about SUBA MAT (the version I play), it feels generally poorly developed. You'll just have to play both and figure out which one you like more for yourself. I do recommend trying CiB M.A.T., I've never played it, and I've invested far too much in SUBA MAT to crossover, but I've heard that it has a much larger player base and even more content.
