Post the best wi-fi games here. Oh, and everyone who posts Pokémon, only trading, is a bonehead
If you can use a simple patching program, download Jump! Ultimate Stars and the english patch. It's sort of like a 2D Anime based Super Smash Bros. type of game. Up to four people in a fight, and everyone just fights to the death. It's a pretty interesting game, and it has open WiFi so you can fight anyone from around the world.
If Metroid were the same way now as it was from its release up until about one year ago (which is when I stopped playing actively, 6-8 hours a day), I would definitely say Metroid was the best back in the day. Too bad it is not. I remember not being able to go through 2 hours without one good game--every game was either a disconnect or a hacker. Good ol' friends that I like to call "veterans of the old generation" (lol) do not play anymore either, so I do not find much fun in the game anymore. Yu-Gi-Oh Chamionships 2008 is pretty good online, and like Metroid, not as good without the Wi-Fi. At first, I played without wi-fi, and after getting bored, found a code that would mean getting every single card, then put together a few decks and went on Wi-Fi, which I put most of the 70 hours that have into doing. I'm not a Yu-Gi-Oh expert and like Metroid much more, so the time I spent playing the game is considerably less. You can always find someone to duel. Other than those two, I spent sometime with Custom Robo Arena, which also had a pretty decent storyline that I played through twice. The Wi-Fi, which this post is suppose to refer to, is pretty good too, with all the strange strategies people can concoct. However, in some aspects, the different parts deal more with luck and power more than pure strategy, even though most sets are made for completely strategy. This is because sometimes your opponent has a set that completely overshadows yours, and there is no way to defeat it without your opponent being a twit and you having very good timing. And since one can only have one gun, it isn't like Pokémon where you can switch to a counter. Or you can rely on the weaker pods and bombs, but they don't help much most of the time. There have also been cases where I haven't found anyone online to play, but then again, I haven't played in about half a year.
I personally say Mario Kart or Metroid, but you never can't fight good for an half hour without a hacker or disconnecter