the_green_dragon said:
I would recommend getting either Heart Gold or Soul Silver. It will keep you busy longer, since it is technically twice the game because of using two regions, plus, being a remake, there is a whole lot of extras that weren't in the old gold and silver. Plus as an added bonus, the games take the Pikachu follows behind you mechanic from Yellow and blows it out of the water by allowing you to have any of the hundreds of Pokemon follow behind you, all you have to do is have that Pokemon in your first party slot, also you can then talk to your Pokemon to get different bits of dialogue and it sometimes gives you things it has picked up.
The only thing I would say about the first Black and White, eventually get one, because they are great as well. Yes, you can't get the original 150 right away, but contrary to what detractors will say about the new Pokemon, they are actually really awesome. I've created four separate teams of 6 just from the new Pokemon(I did that because of all the people saying they looked stupid and they weren't as good as some of the older ones, which frankly, I find them better than most of the originals). Also, one of the biggest changes to the series came in B&W, and that is that TMs are no longer one time use. They've become like HMs have always been, but unlike HMs, you don't have to get some NPC to delete them for you. Basically, once you get a TM, you will always have it to use on whatever Pokemon you want to have the move. I think this change was long overdue since it made it so I didn't have to grind to get money or points to get multiples of a TM; I hope the change is here to stay.
Last, on what games have what Pokemon. It has always been the case with each iteration after the first generation, that you can eventually get all the previous Pokemon, through trading and whatnot.
Also on your Platinum question from earlier. What that 495 number means is that you will through capturing in game or through trading, the game has the space in the Pokedex for all 495 Pokemon that had been created since first gen to then, the fourth gen. Out of that 495, I would say that 60 or so various Pokemon you will have to trade to get, because with each generation, there are at least 15 version exclusives.
Oh and I almost forgot to mention about Heart Gold and Soul Silver, there are more than the 250 total that were in gen one and gen 2. Through certain conditions like swarm Pokemon and such, will be able to capture some gen 3 and gen 4 Pokemon in game without having to trade from a gen 4 game.
Finally I will impart this information to you:
http://www.serebii.net/index2.shtml
If you want to know anything about the Pokemon games and other things, that is the place to go.