A accelerated a1200 or a a4000 is probably your best bet when it comes to being compitable with both classic and more recent amiga games.
An 1200 with a accelerator and HD will work with 90% of a500 games as well, when installing the games to a hd using a program like whdload. This will also mean no floppy swapping and very fast loading times. A pre aga machine like the a500 will not be able to use newer games that use the much more modern aga graphic chip. So the a1200 is a much better bet in my opinion.
The a4000 is basically the same, just that it is more easily expandable thanks to it being in a bigger case with expansion slots. The a4000 is however more pricy and the a1200 can be expanded just as much if you tower it.
