I replaced all the copper in my 50 year old house with PEX because the copper had sprung pinhole leaks in many different places, including the fittings (which were done with the old 50/50 lead/tin solder). Of course, I am on well water, which is quite acidic (about pH = 5), so this explains the leaks.
I used Wirsbo PEX, and originally used brass fittings, but about halfway through switched to plastic fittings. I bought the expander tool, which cost about $300, well worth it, since I ran about 200 feet of pipe, both 1/2 inch and 3/4 inch.
A word of advice on PEX. First of all, you need to use potable water class PEX for your drinking water supply, not the PEX used for underfloor radiant heat systems. Second, check out the threads on the lawsuit related to PEX brass fittings made by ZURN. Apparently ZURN sold over 100 million brass fittings, some of which failed shortly after installation, allegedly due to improper design or fabrication. ZURN is apparently no longer reimbursing plumbers who installed these fittings. I do not know if ZURN makes brass fittings for PEX anymore, but they may still be in warehouses or stores.
If you elect to go with plastic fittings, note that they cannot be reused, so if you need to add to a line and remove a fitting, you will need to throw the fitting out. No big deal, they don't cost too much.
Theoretically brass fittings can be reused, but my experience was that in order to remove them, you had to cut the plastic off with a utility knife, which was sufficient to damage the fitting and cause a leak if reused. Best to plan on throwing them out if you ever remove them. So when you install your pipe, you might plan to get some extra fitting, especially unions, since you may end up removing one or two fittings along the way.
