I would be inclined towards the MSC itinerary.
MSC is becoming more popular with Americans ditching regular marques e.g. RCI, Carnivcal and in particular Celebrity, where they would normally book suites. They are going for MSC Yacht Club which is very much up market and like being on a ship within a ship with access barred to non Yacht Club cruisers. Top service and inclusions. MSC is certainly not formal in the Cunard and UK P&O sense.
I have cruised on MSC and, although, it was not the best as far as food goes (MDR), I look back and see that if I knew what it was like before going my expectations may not have been as high. MDR food was particularly disappointing however I thought the buffet was great.
The MSC ships are wonderful, very classy. Service, at times, was a bit hit and miss in the MDR. Very inexperienced staff with a big work load (late 2019) but that may not be representative of all their ships.
I suggest you give it a go, particularly the Yacht Club.
I'm looking at what's available on MSC in the Caribbean but I have to factor in single supplement to the cost unless I can find a cruising companion.