Agree with this.

Personally I'd put GC ahead of Wii, and Switch yet to be determined. Switch has the advantage that nowadays indies are a thing which provides a lot of third party support, and old ports are a thing as well which is providing some third party support. Those things didn't really exist in the GC or Wii days, and those two things comprise a lot of Switch's quality third party library. Still though, if we're just going off raw 3rd party library and not taking generational context into consideration I'd put Switch in 3rd, GC 4th, Wii 5th significantly behind GC.

I'd have to put Switch first. There is so much legacy content brought over, from every generation. It has gotten pretty good support for current gen to.

I know there are some big franchises still missing, but the Switch has seen many firsts for Nintendo.

SNES
NES
Gamecube
Switch (on the rise)
Wii
N64
Wii U

The GameCube, despite missing a few titles like GTA had a decent amount of support for mainstream AAAs. Hard to really rank the NES vs. SNES as everyone was creating games for the NES, but the SNES had such a killer library of third party games - right up there with the PS1.

The SNES is the obvious #1, after that I'd say the NES and Switch are 2 and 3, though the Gamecube actually had some pretty good 3rd party titles too. The Wii, N64 and Wii U are bringing up the rear.

Maybe, but I feel like that, by the end of the Switch life, he will take NES place, given how good it's support has been.

It's tough, but I would say:
1. SNES
2. Switch
3. NES
4. Wii
5. N64
6. GC
7. WiiU

7. Wii U - It really failed to attract third parties, it lived only on Nintendo's own released. It wasn't all bad though, the first year it got some of the big titles. And unlike previous Nintendo consoles, it had the benefit of indie support.

6. Wii - Considering the success of this one, the third party support is really embarrasing. It either didn't get the cross platform games, or it got weak versions. It's exclusive third party titles were often shovelware. However there were a handful of really good 3. party titles, such as Red Steel 2, Rayman Origins, GoldenEye 007, World of Goo etc.

5. Gamecube - It actually got a fair amount of the cross-platform titles, however, considering how capable it was, it is pretty weak that it often got overlooked by third parties, and the titles it got barely looked better than the PS2 versions and considerably worse than the Xbox versions. It also barely got any noteworthy third party exclusives.

4. Nintendo 64 - It didn't get the quantity, but it got the quality. It's third party cross-platform titles were often the definitive versions. It also got a lot of third party exclusives, such as Doom 64, Turok titles, WWF: No Mercy, StarCraft 64,
007: The World Is Not Enough, Rogue:Squadron.

3. Switch - It might lack behind some of the others in quantity and exclusives. But the fact that you can take these AAA games with you on the go, is just impressive. Unlike the Wii, the ports for Switch are good quality. It also has better indie support than pretty much any system, another huge plus.

2. SNES - Well it was the king of the market for a reason. It crushed the competition when it came to third party support. I cannot put it first though, because most of the big third party exclusives were RPGs, while number 1 had it all for itself.

1. Nes - So many third party franchises came to existance here: Castlevania, Mega Man, Metal Gear, Contra, Ninja Gaiden, Final Fantasy. It had everything.

Of the libraries I've owned (never owned an NES or SNES so those libraries don't count)...
1. Switch: Largely seventh-gen ports and indies, but there's so much to choose from.
2. GameCube: Some fun games here, even if a lot of PS2 and Xbox games were missing.
3. DS: I played an ok amount of 3rd-party games and they were fun, namely the Scribblenauts games.
4. Wii: Some fun games here and there.
5. 3DS: I've heard the 3DS has a great 3rd-party library, but I think I've only played 2.
6. GBA: Didn't play too many third-party games, but there were a lot released.
7. GB/GBC: See GBA.
8. N64: The N64 was certainly lacking in third-party games.
9. Wii U: I don't think I need to go into detail.

Hm well for the systems that I own:
1 - The Switch (This is a combination of me having the money buy lots of games and the huge variety of third party games on Switch.)
2 - Gameboy Advance - I played almost exclusively third party games on the Gameboy Advance. I love that system.
3 - 3DS - I keep finding more games to play on it!
4 - Gamecube I played third party games the most on this (outside of Smash and Wind Waker). So many hours spent playing Spiderman 2, Rogue Squadron, Sims 2, Call of Duty 1, several medal of honor games.
5 - Wii I skwed a bit more towards Nintendo with this system.
6 - Wii U I got the system too late to have many third party games on it and their aren't that many anyway.
7 - Gameboy/Colour I just never had many games for it.

Probably SNES at number 1.

NES at number 2 (pretty much had all 3rd party support, but SNES had the better library IMO)

Nintendo Switch at 3 as it gets a healthy mix of collaborations, remastered ports, and current gen 8 titles as well from big 3rd party publishers despite not having the same amount of support as NES and SNES.  It also has spectacular indie support however.

N64 at 4 as it does have a good amount of games from 3rd parties made specifically for the console, but quality was all over the place. A lot of gems, and a lot of sloppy games that did not transition well to 3D.

GameCube at 5. This console I have the least experience with, but I feel 3rd party support was around N64 level or a little less.

Wii would be 6 due to having a lot of shovelware, despite having strong 3rd party support overall.

WiiU is dead last, as 3rd parties all but abandoned it before we knew what was going on.

Honorable mention, all Nintendo dedicated handhelds have had great 3rd party support, and consistently, across the board. I will not rank them individually, but I will say they all land in the SNES and NES zone of 3rd party suppory.