Currently Online 
I recently finished the Sly collection and am now halfway Jak 2 in the J&D collection.
I would rate them like this:
J&D precursor legacy
Sly collection in order
J&D 2 and 3
The difference between the precursor legacy and J&D 2 is still too jarring. It takes a while to get used to the transition from the colorful variety with plenty of humor and seamlessly interconnected levels of the precursor legacy to a dark Jack moving around in an annoying gta style overworld. It's fine once you get to the platforming but the crap in between is a big let down.
Sly cooper also changes quite drastically from the first to the other 2. The first one is pretty much a pure 3D platformer, while 2 and 3 focus more on story and have you do different tasks with different characters. The style remains the same however. (Apart from Carmalita's voice, did not like her voice actor in part 3)
You can't go wrong with the game play of either though. I would say Sly is slightly more forgiving in platforming then J&D and has a bit more variety and content. Yet the charm of the precursor legacy makes it stand out even above R&C. Speaking of R&C I'm also looking forward to replaying those games when that collection comes out.
Btw replaying these games in order is quite the eye opener in how ps2 graphics advanced during the generation. The difference between the first and last games in the series seems a generation apart.
