For the 3DS, you really can't go wrong with X or Y. They redesigned the game so new users could pick it up and play and dig right in and I've been loving it since I just got it over the weekend. I don't really have any GBA advice, but the later versions are usually the better versions according to friends.
I've played all of them except the ruby generation and Emerald seems like a good one to get into as it was way more engaging for me. Pokemon Black was also the most challenging Elite Four wise since the first gen.
I'd recommend starting with the earlier ones. They might be a bit out dated but at least you'll see what the whole thing started with.
Thats a hard question, but a beginner like you, I'd have to say start out with Leaf Green or Fire Red, and then Ruby or Emerald, then work your way up to the 3DS versions like White and Black, and X and Y. Trust me when you start playing, you'll become addicted.
Pokeomn Pearl is the best last game they released. The newer versions are filled new stupid pokemons. Try this or even go back to Greenleaf/Fire red
Pokemon platinum and Emerald is the best I think. They are fun to play and have a very good storyline that will keep you entertained for hours.
X & Y is probably your best bet for now. It's gotten a lot better and it plays a lot better also but if you want to experience the original Pokemon vibe I suggest you get Platinum for the DS.
I agree. I think X&Y is probably the best one you can get now so far but if you've never played any of the other Pokemon games before then it's a good way to start off with the classics.