I've seen em both(I've already bought AC so downloading it is legal for me in my book!) and I enjoyed AC more. TSW was great and all, but kind of a let down at the same time, just because it really didn't end well. I won't say more about it.

AC had a great opening, had all my favorite characters, and basically brought the world of FFVII alive again. Plus, seeing Tifa kick someone in the head(you can see that in the trailers) always is a plus.