>>56538429if you're only gonna play one, just pick whichever looks best between Emerald, Platinum, and Heartgold/Soulsilver.
if you plan to play multiple, start with Firered Leafgreen, then Emerald, Platinum, HGSS.
I would just stick to Gens 3 & 4 unless you're really interested in the retro games for curiosity's sake, but most people are probably gonna have more fun with the remakes these days.