I still recommend getting Black first. 90% of Pokemon players are not super obsessed fans like most of us, and are fine with playing one game every 3 years or so.
And then if you like it a whole lot and hae played it and want more, then go back and get Platinum. And if you STILL want more, get HG or SS.
Gotta agree with this.
Of all of the main games, Black/White is probably the friendliest to beginners. For one, unlike in previous generations, it's
exceedingly difficult to go wrong with picking out pokemon for your team. It'll also make sure you get to know the basic aspects of gameplay and does more than any other game to help the player along (though just how much of that help you utilize is, of course, up to you). Some feel as though that's something of a step back--I disagree, for the record--but for first-time players, I feel that makes it the ideal first game, and a good introduction to the rest of the series. Really, the only thing you'll be missing out on is a couple of minor references to previous main games, but that knowledge is in no way required to enjoy it. Either way, get one of these (either one, it doesn't matter) first.
Platinum is, in my opinion, pretty much the overall best of the lot. A good second game, if you want more. Just one thing to watch out for: since Platinum is from Gen 4, there are some gameplay advancements made in the Gen 5 games (Black/White) that will be absent. Most notably: TMs. You'll figure out just what these are when you start playing, but the gist of it is: in Black/White, these were made into infinite-use items. They are
not infinite-use in any game before Black and White; this includes Platinum and Heart Gold/Soul Silver.
And speaking of Heart Gold and Soul Silver...well, they aren't
bad games. It's just, even though they may be the easiest main-series games as a whole, there are certain flaws that make certain parts...decidedly
not friendly to beginners. Mostly it has to do with a level curve that, put simply, leaves most boss fights severely overpowered compared to the player, most other battles severely
underpowered compared to the player, and the player him/herself with meager options for grinding experience levels. Combine that with a story that's weak even by Pokemon standards, and you have something that I cannot seriously recommend to, well, any player over Black/White or Platinum. (...or Fire Red/Leaf Green or Emerald, for that matter.) At least, not as your first game in the series. Pick it up if you're really that interested, or just to see what all the fuss is about (since something like 90% of the folks here seem to positively
adore these games for some reason), but I definitely say save it for after the other games I've talked about here.
So, uh. Yeah, hope this helps with your decision!
(tl;dr: Just read randomspot's post again.)