I am going with Sly Cooper. I have not played the sequels yet, but I immensely enjoyed the original game to death, and I can safely say that out of these three, it is definitely the best platformer. It's rare for me to throw praise towards a 3d platformer, but Sly Cooper and the Thievius Racoonus is just plain awesome shit.
While I do think Ratchet series is good stuff, they pretty much fail when it comes to platforming. Yeah, Sly isn't that much difficult either but who cares? It still places a greater emphasis on platforming.
I've never been a Jak fan to be honest.
It's really interesting to see American developers kick the pants off of the Japanese developers when it comes to platformers these days. Hopefully we get new platformer IP's next gen, Sony or whatever.