First of all, considering how the 3DS has been out for three years compared to the Wii's roughly 6 years of receiving games, I think this is a terrible comparison. Of course the Wii will have the upper hand: it may have been a front-loaded system, but the Wii, in the second half of its life, got games like Super Mario Galaxy 2, Skyward Sowrd, Xenoblade, two Kirby titles, Rayman Origins (a decent version), Rhythm Heaven, Donkey Kong Country Returns, Sin & Punishment, a then new Monster Hunter, The Last Story, some nice shooters like Red Steel 2, CoD, and Goldeneye, Epic Mickey, Mario Party 9, Silent Hill, Sonic Colors, etc, etc.
If we compare the first, say 13 quarters of the two systems lives' to each other (the Wii Q4 2006 to Q1 2010 and the 3DS Q1 2011 to Q2 2014), we get a much more interesting answer:
- Action-Adventure - Tie. The Wii obviously had Twilight Princess, but most of its other notable games in this category, like Bully and whatnot, are ports.In addition to borderline shooters like Kid Icarus and Resident Evil, the 3DS gets Luigi's Mansion 2. To close to call, especially considering how TP was a GameCube game also.
- Adventure - 3DS. Zack & Wiki is okay, but the 3DS has two Layton games, Ace Attorney, and Zero Escape. No contest.
- Fighting - Wii. The 3DS had Street Fighter and Dead or Alive, but has had little else since 2011. The Wii had Brawl and various quality Anime fighters. Plus a vs. Capcom game.
- Music - Wii. The Wii had much Guitar Hero and Rock Band. The 3DS has Theatrrhythm. The end.
- Platformers - Wii. The 3DS is not lacking in this category, but a few key Wii games stand above their 3DS counterparts. Galaxy > 3D Land, NSMBWii > NSMB2, Wii Sonic titles > 3DS Sonic titles, etc. Each system has their own unique titles (Wario Land vs. Kirby, Mega Man 9 vs. Steamworld Dig, etc), but the equivalent titles give the Wii a major advantage.
- Racing - Tie. Mario Kart exists on both consoles, but there's little else.
- RPG - 3DS, by FAR! Compared to the Wii's virtually non-existent RPG library, the 3DS has Pokemon, Bravely Default, Etrian Odyssey, Shin Megami Tensei, Mario & Luigi, Tales, and Paper Mario. Say what you want about Xenoblade, it was one game, and it wasn't out yet.
- Strategy/Simulation - 3DS. The 3DS has the better Animal Crossing and Fire Emblem games, Shadow Wars, Rune Factory, Harvest Moon, etc. Sorry Little King's Story, you're not enough.
- Shooters - Wii. The 3DS has three great shooters: Kid Icarus, Star Fox 64, and Resident Evil. One of those is a port, and the other two are practically "Action-Adventures." The Wii had Metroid Prime 3, some decent Call of Duty, games, House of the Dead, Resident Evil games of its own, and Red Steel 2.
Once again, the Wii comes ahead, but this time only marginally (1 point, less if you consider the weight of RPG's).
Ultimately, I think the 3DS will have a better library than the Wii because it will get more great games past mid-2015 or so (Late 2010 for the Wii).
