So, for a total casual who dont care about itens, iv, competitite stuff and just want to complete the pokedex, which game you guys reccomend? hgss? platinum? bw?
If you want to make completing the pokedex tough but rewarding, I'll recommend all of gen 3
It's built in such a way that every single game in the generation helps contribute
by being borderline mandatory for a full pokedex in RSE. RSE has the entire Hoenn dex and a lot of Kanto, FRLG fills in the missing Kanto spots and adds some Johto in the postgame, and Colosseum/XD fill in the blanks for what little is left. It's a great way to go through the generation and helps the entire thing feel very cohesive.
Even though it is fucking evil lmao. I cannot imagine how much this must have pissed off parents back in the day.
Additionally, since it's only a little under 400 Pokémon and a whole lot of them have relatively interesting methods of capture
instead of generation 8-9's "oh find them in raids" or "oh they're wandering around somewhere out there", the dex hits a nice sweet spot between "stupidly hard to achieve" and "satisfying to complete." I know I start tuning out when the dex gets higher than 500, anyways, and I've only ever gotten very close to completing Alpha Sapphire's national dex as a result, but I personally find gen 3 to be a pretty rewarding way of doing things and would recommend it any day.
If you just want a quick run-through of a pokedex you only need both versions
or glitches for, though, I'll back Celebrate Nite and offer gen 1. Generation 5 gets close, but the addition of 4 entire generations in the postgame for the rest of the dex makes it a bit hard to recommend in the same way. I will warn you, though, that RBY haven't aged very well and are a bit of a pain to play. They'll be especially hard to tolerate if you started the series in generation 4 or later, but tough no matter what unless you've got really heavy nostalgia goggles for them.