>>51320885^this^
I will warn though that a few mon evolve ridiculously late, so if you want to use a few in a playthrough team you'll be stuck with first-stages for a while (even though most of them are near the end of the game anyways, so you'll be fine)
ORAS would also be decent if you started with gen 3, but if you've played Emerald then I wouldn't recommend it because it will feel noticeably bare in comparison
(also turn off exp share once you get it because otherwise the whole thing becomes hardcore brain-off and really boring to play)
Don't go past gen 7 for mainline stuff (it's not worth it), save for maybe PLA if you want something entirely different but slightly relatable (assuming you play gen 4 beforehand)
and if you want to play gen 4, stick to Platinum/HGSS. DP are by no means terrible, but they're heavily outclassed and have the same problem as ORAS where they feel incredibly bare on revisit in comparison to their third version
if you want to get into competitive for whatever reason, don't play cart. Not worth buying the newest gens to compete, just stick to Showdown or something (not a compfag myself; might want to bug an actual enthusiast for good advice)
also also, if you still have your gen 3 games, you can actually transfer them up into Platinum! I think it's pretty late into the story, but you can still have your bros with you if you wish
I think that's about it. For spin-offs I'd say try Ranger (1 or 2), PMD (1 or 2), or Conquest and then don't touch anything else; it's not bad, but those three are the ones I'd say are really, properly good instead of just enjoyable or mediocre.
Have fun anon, but try not to get too attached haha. This series is going into the shitter, i'm just here to watch it burn and draw the new designs for practice.