For me it's...
Sony: PlayStation 4 easily for numerous reasons. First and foremost, unless I'm mistaken, between AAA releases and indie games, I believe the PlayStation 4 can play more games than any other system in history, and what's more most of my favorite games ever are available for it! On top of that, it's also got IMO the best controllers out there, and furthermore remains among the most high end systems released to date in terms of graphical capabilities and all that to boot. This has also been a console generation that's really seen Sony come into their own when it comes to all-around compelling first-party releases, from Uncharted 4 and The Lost Legacy to the new God of War, Horizon: Zero Dawn, and well beyond. These games aren't just fun to play, they also have excellent storylines and so much more that go to prove the ongoing merits of single-player games in particular here in an era where they more largely seem to be fading into the background. It's also to be the exclusive home of my most anticipated game ever, The Last of Us Part II, and furthermore also the exclusive home of what is, for me, this year's most anticipated release as well: Death Stranding. PS4 has also had the best, most playable versions of many non-exclusives too.
Nintendo: Switch easily. In addition to some of the strongest first-party support I've yet seen Nintendo offer any of their systems, the Switch also now boasts a highly expansive indie library that includes many, many of my all-time favorite games, plays NES and retro arcade games too (as well as a handful of other old-school titles), and is also portable to boot. That last item is extra cool and distinctive!
(Like I've said before, I consider this current era to be the best in gaming history.)
Microsoft: Xbox 360. Whereas I hadn't been too impressed with the original Xbox, Microsoft had me right out of the gate with the 360, which released with such exclusives of appeal to yours truly as Perfect Dark Zero and Kameo: Elements of Power and quickly become my 7th gen platform of choice by beating the PS3 to the punch on numerous major and/or just awesome titles, including such examples as The Elder Scrolls IV, Portal, Mirror's Edge, Braid, BioShock, and Mass Effect. Even Final Fantasy XIII got a same-day international release on the 360. (Also, I thought Banjo-Kazooie: Nuts & Bolts was cute.) Only from the second half of the 7th generation did the 360 start to become my second choice for that period.
Sega: Saturn. In a technical sense, the Saturn wasn't the highest-quality 5th generation console released at all, but it had a number of exclusives that I still enjoy playing today, including Magic Knight Rayearth, Shining Force III, NiGHTS Into Dreams, and the early Panzer Dragoon games. Not that this means much in retrospect, but the Saturn version of the original Tomb Raider was also the first version of that iconic game I got because it came out a whole week before the PlayStation version here, so a lot of my first memories with the Tomb Raider franchise are tied to the Saturn.
Yeah I'm pretty sure that what you said about the PS4 isn't true with all the games they added via backwards compatibility the X1 has just as many games available as the PS4. The console that could play the most games was more then likely a early PS3 with full backwards compatibility since it could play all PS1, PS2 and PS3 games.