For the gaming A600, I use a C= 1084-S, but that's only for games.
A2000 uses a Commodore 2080, since I like to run Workbench interlaced, and the 2080 is a natural flicker-fixer. I don't guess it's ideal for games, but it doesn't look bad -- I play Super Street Fighter on it regularly.
A4000 & 3000 share the Commodore 1950 @800x600. I also have a 1960, but for some reason the picture just don't look as good to be as the 1950...