We have been on about 20 of the cruises out of West Palm Beach, on the 3 ships that have sailed out of there since 2010 or so. It is a matter of convenience, living about 20 miles from the port. I figured that Margaritaville at Sea would eventually have the 2 for 1 fares, to try and fill the ship.
Since you primarily sail Princess, it would be best to not have high expectations for Margaritaville. It is a 30 yo ship, with few of the amenities that the larger, newer ships offer.
A couple of things that we do like:
Wine tasting on first day, champagne breakfast first morning, (if still having these) and usually a decent band in the evening in one of the lounges. Also the cabins are rather large for the size ship.
Over the years, we have gotten to know several crew members and look forward to seeing them. Look at a lot of review videos, as there were several media cruises, with opinions positive and negative. Good luck!!
As for MSC, is one of my favorite cruise lines, having been on 4 MSC cruises, 3 booked for next year. They are very international and a lot of the guests are from Europe. They have a very different pricing structure than other cruise lines. I could go on, but this is not the MSC forum.