I have no experience with PEX; can't comment on it.
I plumbed a house using PVC for pressure and drain piping. It is easy to use; about all that you need for tools is a measuring tape, a hacksaw, a pencil, a utility knife to remove internal burrs from a cut and a coarse file to remove external burrs.
You can buy adaptors to transition from PVC to galvanized or copper.
The plumbing is about 16 or 17 years old now; works fine and makes no trouble. It's easy to break into a line and set up another run such as for an outside hose tap, insert whole house and drinking water filters or plumb in a water softener. If you change your mind about the layout at any time, it is a simple matter to remove what you don't like and do it over.
While doing the work you can stop where you are, cement a cap on the end of a pipe run and turn the water on after an hour. The next day you can saw the cap off and continue where you left off.
My neighbor left his house for the winter after blowing the pipes out with air. He did not do one run quite well enough so the water in the pipe froze and split the pipe. It was a cheap and simple matter to graft in a repair section using sleeves.
A large array of fittings is available including sleeves, hose bibbs, corners, tees, transition pieces etc. The piping and fittings are inexpensive.
The cementing of joints process was totally reliable for me, no leaks.
I have no complaints about water delivery speed. Our bathtub fills a little slowly but that is due to the small orifices in the temp controlling faucet.
Make sure that your code permits PVC piping.
Modified by Tinker Toy at 2:50 PM 3-1-2010