We, too, have done both Yacht Club and Haven. I agree that I would not be impressed sailing on MSC outside of YC (we were on Belissima from Genoa early in her career). On NCL I have sailed both in and out of Haven and would do so again. Hubby is sold on Haven. The reason MSC prices have been so much more affordable than other lines is because they were trying to break into the US market, in my opinion. Now that they have established some reputation, I think that is why the prices are headed up.
Have always felt at home in the Haven. The YC was wonderful space, with string quartets playing in the lounge some nights. We were in the largest suite, so the Maitre d' bent over backwards to ensure we were pleased with the food/wine. Haven has those wonderful 2 bedroom suites available for families, with the extra full bathroom. The OS on MSC only had a single bathroom, even though there was plenty of space in the stateroom for more than 2 people! We recently sailed in the Retreat with Celebrity. We were on an older ship, the Summit. Stateroom was lovely, but bathroom rather cramped. I like the Haven idea of having everything you need in one area (of course, not all of the ships have the restaurant and bar in the Haven area). The Retreat on Summit included a separate area for Retreat guests, but not on the same floor, and restaurant in one area and bar/concierge in another, not even near each other. I would sail with any of them again, though! (But MSC cruise points expire after 3 years if you don't keep sailing, so that's a downfall. We sailed under the matching status, so were top tier. With pandemic, we haven't sailed with them again.)