The best brand of PEX is rumored to be Wirsbo, which uses expansion style fittings. I'm not sure if they make an adapter to go from copper to PEX or no. The crimp style fittings have an adapter. I would not use any of the push style or compression stye fittings. Use either the Wirsbo expansion fittings with the correct tools or the crimp style fittings with the correct tools. Many of the crimp style fittings have a crimp they call qickclamp this is not an automotive style clamp, never use those. They are a crimp that one tool does several sizes.
Zurn has a law suit against it for their brass crimp style fittings breaking due to some water conditions and the foriegn fittings not holding up. I use Zurn because the corperate office is closer to home, but I have been unable to get a response from them about the suit. Kitec is another brand that is having legal issues. The pipe all seems good as long as you stay away from the al types and go straight plastic. My advice is make the fittings accessable, they seem to be the issue. Copper can have issues too, so it is not perfect, in my opinion PEX is the best thing going now, just don't put fittings in the wall and don't put the pipe ot fittings in a bind, allow a lot of room for expansion and contraction.
Go to Zurn's website they have a really good how to on the crimp style fittings and installation.