I used to use the fusion pack v10 myself. Some fine models it had. Some of em were weak, but the grenade effects are 10x better than that of standard CS.
When I was good at CS, I had an awesome Colt model. The gun model was in the +1000 in poly's and had a beautiful skin. But what made it special was the sound. For some reason, it drove me to aim at the head more and to burst fire correctly, because it was much easier to distinguish between each shot fired.