Probably fifth and sixth gens (PSX-PS2 era), for three reasons:
graphics - there’s something about art styles used at the time that aged surprisingly well and is just pleasant to look at, even compared to later games.
variety - both gens were filled with mid budget titles trying out new, often weird ideas that didn’t always work but can be really interesting even to this day (as long as you can overcome jank usually present there).
(least important point) there’s a lower chance I’ll find games from this era to be too old-school for me. I have a high tolerance to old game design but I’m not immune to it. Sometimes there is such thing as “too old” and that’s alright.