In my opinion, CFS2 is a much better game.  It's true that CFS3 has better graphics-but thats about it.  CFS2 has less problems and has a far better compatibility with 3rd party addons.

Now, with that said-if you can get CFS3 to run good on your computer it's a fun game.  I enjoy playing it quite often but if I had to choose one of the two-I'd say CFS2 without hessitation.