"Best" Amiga gaming system? A plain old A500 with 512k chip and 512k fast RAM. (no foolin). And they're really cheap to buy (ask redrumloa for one, he has a whack of them, brand new and he's very reliable).
Then you can always get an A1200 for the AGA games afterwards and you're set [ohh, I have a couple of those too!] :-D
Nothing runs as many Amiga games as an A500.