Oooh, this is a difficult one Foo.
I would say it's between
MOH2:Heroes and a
Nintendo DS.
However.....MOH2:Heroes is a single game (a great looking game by all means - but it's still one game alone). Plus, the main draw is the multiplayer online (the single player is apparently so so).
So you have a multiplayer online game versus....
....a COMPLETE console system. A system with great games like MarioKartDS, LoZ:PhantHrglss etc etc.
As good as a game is (ANY game....even Super Mario Galaxy), it can't compete with having a complete DS and the ability to play LOADS of great games.
Also, a DS and a Wii will allow you to unlock certain content in games such as the extra galaxy in GeoWars....or link together in games like Pokemon....
(I'm sure future games will also make use of the connectivity).
So the choice has to go to a DS....because you get more "bang for your buck".
If you're not too fussed about getting a UK one, places like VG+ and Play-Asia allow you to import special editions like the Zelda Gold Triforce one:
or special colours like the crimson/black one:
As they're universal, all you need is the official UK ninty charger (auto-switching voltage), and they're usually marked as "gifts" or "childs toy" and marked low so that you won't get stung by customs
.
Failing that, I quite like the Black DS's (I myself have a white one, but have heard many reports of these being maybe slightly more prone to cracked hinges).