Harold is a little bit off on limitations for PEX. PEX can handle 180 degrees at 100psi, or 200 degrees at 80 psi. The difficult thing for a contractor who does not have significant experience installing PEX is learning and remembering that PEX expands when heated. On a 100 foot run with a 10 degree rise in temp, copper will expand about 1/9", PEX will expand about 1.25". Therefore when installing it, a plumber must allow for expansion by not fully attaching the PEX or by installing expansion loops in the system.
My recommendation is to look into KITEC pipe, which is a composite pipe. It has an aluminum core so it handles like soft copper, yet has the corrosion resistance of plastic. It has a 30 year guaranty on the pipe and fittings, can handle a ph range of 2 thru 12, is 865 times better insulating than copper, and is very quiet.