PEX is great in most circumstances. I ran PEX for a basement bathroom and my washer and it was fantastic as it is somewhat flexible so if my joist holes were slightly off it was very forgiving (copper would not allow this) or if my measurements were out 1/4" it made no difference - try that with copper. Plus it cuts down on joints as I could do a wide angle bend rather than L's and if I needed a 90 degree turn it was easy - no worrying about starting a fire trying to solder an L between joists. If you make a mistake it is easy to correct. If you need to T into it later it is simple - try T'ing into a long run of copper in a tight space. Nearly all the accessories for copper are available for PEX - though not every store stocks them.
The downside is anchoring it where it joins a fitting. For my washer it was easy as there is a fitting that can be screwed to a stud but for the shower I had to add copper prior to the valve and head so these fittings would be solidly anchored. The body sprays will probably need copper for the same reason but the special pressure balancing plumbing behind these could be PEX. Or maybe your fittings don't have these problems. For the toilet and vanity, PEX was fine as there are special supports you can use (or just clamp to a stud) and it doesn't matter if there is slight give in these.
Hope that helps - I'm planning to replace much of the copper as I redo other bathrooms and kitchen. You can cut PEX with a sharp blade but one of the special cutters is worth the investment if you have a lot to do.