I think Wii was the worst. Not saying it was bad, but compared to the other systems. Surprisingly I have found myself enjoying Wii U's third party titles immensely, even though there are hardly any.

It has been nice to finally be able to play some assassin's creed and batman arkham games! Darksiders II, Injustice Gods Among Us, Resident Evil Revelations, etc. Again, not many, but some real great ones.

- I'm surprised the N64 isn't winning... Seriously, that thing had terrible third-party support. Not a single Square game seals the deal for me (a HUGE deal back then). Konami put those half-ass 3D Castlevanias, while the PS1 (and even the Saturn!) got fucking Symphony of the Night. I could go on and on.

- Gamecube was fine. It was actually the definitve console for Resident Evil fans.

- Wii had A LOT of crap. Because it was weaker, it missed ALL the major third-party games of the generation, which sucks.

- Wii U suffers from the exact same problem. At least it got some seventh gen ports.

So basically (from best to worst), GC > Wii U > Wii > N64

I don't know why some people keep putting the N64 last. In terms of quantity it certainly had the least 3rd party support outside of the Wii U, but in terms of overall quality it actually had a pretty good 3rd party stable of games. Obviously the PS had the bigger exclusives like MGS and FF, but N64's library despite its frequent software droughts was still very respectable all things considered. Here's a few examples of what I'm talking about...

The Turok franchise (exclusive on consoles to the N64), Bomberman 64 / Hero, pretty much all major annual sports series like Madden and FIFA and even a few sports exclusives like NFL QB Club, Ken Griffey MLB, NBA Courtside and Wayne Gretzky 3D Hockey, a bunch of quality Star Wars titles including Shadows of the Empire / Rogue Squadron / Ep. 1 Racer / Battle for Naboo, the THQ WCW/WWF games (still considered some of the best wrestling games ever), niche RPG titles like Harvest Moon 64 and Ogre Battle 64, and other top 3rd party multiplat releases like Rayman 2, Shadow Man, Tony Hawk 1-3 etc.

It even featured great ports of top franchises on PlayStation like Wipeout, Ridge Racer and RE2 with enhancements, and some top PC titles such as Command & Conquer and Starcraft 64 (exclusive for consoles).

N64 enjoyed decent 3rd party support up until the fall of 2000, then support for the console was abruptly pulled, and not just from 3rd parties but from Nintendo as well to focus on GC, with just 2 major N64 releases in early 2001... Paper Mario and Conker's BFD.

Definitely the Wii U. I mean after the first year almost all of the third party developers stopped supporting it.

GC was best for third party
N64 was worst for third party

The Wii U is actually the worst. The system is underpowered so it lacks the major third party because they refuse to downport. The Wii gets off because it was market leader and third party made exclusives to cash in on the non-gamers who bought the gamecube in cheap games. The

Quantity

1) Wii U (worst)
2) GC (Second worst in third party support)
3)N64 (Third worst third party support)

Highest Quality in third party exclusives of the lesser selling Nintendo consoles (subjective in other words imo)

1) N64
2) Wii U
3) GC

GameCube ( easily)> N64> Wii> WiiU