Ok, so looking at the ones I've owned, and in relation to the amount of classics, hidden gems and general amount of games:
1st. DS. By far the strongest 3rd party library out of all of the Nintendo systems I've owned, not only in terms of quality but also in quantity. GTA Chinatown, Etrian Odyssey, the definitive version of Chronno Trigger, the Castlevania DS games, TWEWY... You can find dozens of hidden gems easily enough, especially if you like JRPGs.
2nd. Switch. Best 3rd party lineup thanks to being the default port machine of this generation. Most PS3/360 games are going to end up ported there eventually. What holds it back is its lack of more current games, a library needs more than ports to shine.
3rd. GBA. Great solid lineup of 3rd parties. Very similar to the DS only it has a more limited amount of games. Still, it gave us games like the Megaman Zero series, Sonic Advance series, great ports of Final Fantasy I-VI (minus III for some reason)...
4th. 3DS. Great library overall, but it lacks in terms of heavy hitters. Other than a couple of big 3rd party titles like Bravely Default or the Monster Hunter games, most 3rd party titles are either budget titles or niche JRPGs, which, while ok, is not enough to make it stand out.
5th. Wii. The Wii has one of the largest libraries of any Nintendo system, which grants it a lot of good games, like No More Heroes I-II, Sonic Colours, Muramasa TDB... However, the sheer amount of shovelware bloats the library, and makes finding hidden gems rather difficult. The DS has a similar problem, but it ended up having better games overall, maybe because the Wii gave many devs a "follow the leader" mentality and just added motion controls, whereas the DS's gimmick was easier to implement. Also, the Wii is THE definitive version of Just Dance machine, with only the Switch being close to it, so take that as you will.
6th. GameCube (because the Wii is BC). It has a decent amount of great 3rd party games, but outside of them, there are very few hidden gems.
7th. GB (because the GBA is BC). In terms of 3rd party games, only Tetris comes to mind. Other than that, most Game Boy games are either shovelware, or bad versions of NES/SNES/Arcade games.