Never owned a Vita, so I'm just going to rank the 5 systems I do own.
1) PS2 - This is the system that had it all, quality, quanitity, and variety. In fact I'd say it was the best PS system when it comes to quanitity and variety of games. Only one system beats it in quality.
2) PS1 - This takes the crown on the quality side. Two of my top 5 games of all time are from the PS1 (and two more are PC exclusive). That really makes it the king console in terms of pure quality. However, I didn't play a ton of games on this console. Objectively speaking, I don't think it handles action games very well, especially when compared to the other PS systems. So it was severely lacking in variety, IMO. It technically had a lot of games, but I didn't play many.
3) PS3 - I played quite a few enjoyable games on this system. Overall I don't think it had the quality of the first two Playstations though. The library was smaller, and I also felt like it lacked variety in a lot of ways compared to the PS2. Most notable games seemed like they were shooters or RPGs (or RPGs where you shoot things, or shooters with RPG elements, etc...). It lost a lot compared to the PS2 especially concerning the games that I cared about. Either the franchise lost quality or we just plain didn't get an entry (Final Fantasy, Spider-Man, Ico-series, Kingdom Hearts, etc...). This system is mostly redeemed by the Souls games and a few other unique titles like Valkyria Chronicles.
4) PSP - There were several games I really enjoyed playing on this system. None of them make my top 50 of all time, but I still enjoyed myself.
5) PS4 - This is the most disappointing system I have ever owned. It is even worse than the Wii U, because I expected to be disappointed by the Wii U. Every game seems like a rehash of previous generations. Where is the new gameplay? There isn't any. It's all just sequels or maybe a new series that feels a lot like other games you've already played. The only game in my top 50 from the PS4 is Undertale and I played that on the PC first. The main reason I have this system is for streaming and watching Blu-Rays and playing maybe 1 game per year. So disappointing.