If you want an A500 for classic games to be played from floppy disk your best option would probably be an A500 with Kickstart 1.3 (or 1.2) + 512K expansion. (512K chipram + 512K Slowram).
If you want a classic A500 to use WHDLoad your best oprion will probably be an A500+ with a 1MB trapdoor expansion & a harddrive/fastram expansion such as an A590 or the Kipper fastram/compact flash IDE board & upgrade the kickstart to 3.1.
A500+ has the advantage that it can address 2MB chipram WITHOUT any expensive MiniMegi chip or similar. The A500 can only address 1MB chipram as standard.