Depends on what you consider fun, and how much you, in the end, want to spend.
For my money, E46 M3 and E60 M5. Two of the most flamboyent engines of the last 30 years. And who doesn’t like a V10.
Failing those, i’d probably get something rare-ish, maybe hunt down an unmolested e30, Mk7.5 GTI, or something proper “exotic” like a 205 GTI.
Of course, as a big JDM fan, i’d be scouring through JDM lists too, lol. Maybe one gets lucky and a decently priced first generation GT-R (GPC10 Hakosuka) turns up, that would probably be the dream, for me.
Failing that: ol’ reliable. Miata. Cheap, still one of the best gearboxes to play with, not stupid fast (stock) but plenty. Always a good choice.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.