Having been on both ships, we would definitely choose the Volendam. We loved the Noordam when we sailed on her (5 cruises from '87 - '94), however she is getting old and the cabins are much smaller, unless you go for an A,B or C. She's is a smaller more intiate ship, but I understand there have been a lot of plumbing & A/C problems in the last few years. Also there is a definite shake at the stern of the ship - this was a problem also with her sister ship, the Nieuw Amsterdam.
We sailed on the Volendam at Christmas (had sailed on the old Volendam back in '81) and just loved the her. Cabins are larger, furnishing nicer and it has 2 pools, one under a retractable roof. Niicer dining room, larger show lounge & Lido - just a very nice ship.
Whichever ship you choose, have a great time.