So yea, I like Pokemon games, even if they are "the same game" there is always something in each one that make me want to play, don't know if it's about nostalgia or something else.
But it's not like I have played a lot of them, I skipped whole DS generation because it was too expensive for me back then but, somehow, I got 3DS some time ago and it occured to me that I could go "back in time" and get one for the DS... :) Now, they are not as cheap as you would expect, but you can find "occasion" from time to time (unless it's bootleg > >).
So, with a little hunting I could get one... the question is, with one?

Saying that, we have to keep SoulSilver and HeartGold out of this as they are very rare here, and the prices sometimes are just insane. To be honest it's the one that I would want to play the most (I had Silver back in the days, that ended up to be a bootleg > >... and I have no idea what happened to it) but... oh well... cmon nintendo e-shop...

So in the end we have:
- Diamond/Pearl (and Platinum I guess)
- Black/White
- Black 2/White 2

I wonder if there is any reason I should go for one instead of another. Or maybe it's now worth when I already played "Y"?

I haven't played any of the others you mention, but I wasn't all that impressed with Black \ White.. felt a bit generic and boring..

Unfortunately Heart Gold and Soul Silver would be the ones I would go for as while I haven't played the remakes, the original Gold and Silver are by far the best in the series IMO.

Platinum is the first Pokémon game I ever played and it completely put me off the series. So much time wasted doing things, battles are slow, moving around is slow, there's a ton of legendaries to catch most of which are pretty boring, lots of them are roaming too.

Luckily, I later played X and finally it clicked how great the series can be. Even going back to play the older ones, Gen 4 was a pain. SoulSilver was the last one I played, and while it was better than regular Gen 4, I think a lot of it is nostalgia for the time when I watched the anime and knew all these Pokémon, I don't think you'll be missing much by skipping those, just a nostalgia itch that will go unscratched.

Black/White is the answer. They did something kinda interesting with the evil Team you fight in this game, specially the way they merge that plotline with the Pokémon League at the end of the game. TMs can be used multiple times, and other small quality-of-life improvements were introduced there. They say it's all the same game, but playing all of them and having a favorite and least favorite game, really shows how these little changes can affect how much you enjoy the game.

Black 2/White 2. Also pretty great, has a nice collection of Pokémon from multiple generations, and is probably one of the games with the largest amount of content in it. Might just be my favorite. But it is the only direct sequel in the main Pokémon games, so a lot of characters and events from the previous game will be mentioned which newcomers might not get. So, while I do recommend playing it, it's better to play Black/White first.

Bulbasaur.

I'm going to have agree with DaCostaBR on this one. Black/White 2 is by far the best Pokemon game available (especially given the post-game content), but it's far more satisfying if you play Black/White first. The story in Black/White 2 is a direct sequel to Black/White and really builds on the settings of the original. It's just awesome to see how much the world has changed between the two games!

Is that a trick question? The remakes of Gold and Silver, Heart Gold and Soul Silver obviously, 2nd gen had always been the best (at least for old-timers who saw through the series in its entirety). In them, you can have any creature follow you on the overworld map, too.

If you are only getting one go with Black/White 2, it has plenty of mini games ranging from a area with puzzle battles to a world tournament with every gym leader and champion in every game up to that point, and it has the musical... In addition it has a lot of areas and a fair spread of Pokemon.
If you can get another I would go with Platinum, the problem with Black/White is that while the story is good it has very little post game stuff and no older Pokemon. In addition a lot of the replay ability relied on multiplayer.
Platinum on the other hand has a very good spread of old and new Pokemon, my favorite set of gym leaders due to how each one is integrated into the world. You have a father and a son as Gym Leaders, two friends and one that a wrestler. No forgettable ones (Glares at Gen 2 and 3). It also has the underground and a good amount of post game stuff. As you may be able to tell this game is my favorite due to the world building, and Lucario.
Now, this is not of the main series, but I would try Explorers of Sky. Its a rouge-lite dungeon crawler where you are a Pokemon, and it has a very good amount of post-game and a excellent story.

i would say PMD2 and SPMD for 3DS. but i personally got sick of the original pokemon series after gen 2.

Siralim 2

Black 2 is your best bet, then. You can't go wrong with that one...

Heart Gold/Soul Silver are pretty great to get nostalgic and have a lot of content.

Black & White improved on pretty much everything, I like its animated sprites better than the current 3D models. Also, N for best Pokémon character.
Black 2 & White 2 are perfection when it comes to music and bonus content - the world tournament is a dream come true. Keep in midn that this is a direct sequel to Black & White, so you get the most out of it if you already played the first game.

Yea, decided to go with White 2, it's working for me also because they seems to be the cheapest one for some reason (but not cheap).
To be honest, if most people here would say that the "Platinum" or "Diamond/Pearl" is way to go I would be worried (but, atleast, they are still not near the SoulSilver/HeartGold prices). :P

Well, it's the cheapest one firstly because it's the newest, and secondly because it's a sequel and most people wouldn't play the sequel without playing the first one. I still think you won't like the game as much as all of us who have recommended it, since you haven't played the first one, but at least there's no denying the game is good regardless.

Why did you go with White and not Black though? And have you chosen a starter yet?

pokemon gotta buy em all...it was my destiny,,..but i had no money...