I travel solo and used to sail in the Haven (courtyard penthouse) but it is ridiculously expensive now. I tried MSC YC first 4 years ago and as others have said there are pros and cons for each. However I prefer YC as I think the service is better and I like that everything is included ie Premium drinks, Premium Wifi and Spa access. They have changed the minibar inclusivity (now there are only refills on the soda but you do get a litre of a spirit). I stay in an interior as spend very little time in my cabin.
Here is my quick comparison
Haven
YC
Priority check-in/boarding
y
y
Butler escort off ship
y
y
Butler escort back on ship
n
y
Butler escort to shows
y
y
Wifi included
n
y
Drinks included
y
y
Spa included*
n
y
Grill on sundeck
n
y
Restaurant menu changes
n
y
Daily snacks in lounge
n
y
Lounge entertainment
n
y
Daily snack delivery to cabin
y
y
y
* NCL only if in spa cabin
One thing to note with MSC is that you can't make speciality restaurant bookings until you board.
The things I prefer on MSC are:
Everything is included, the spas are amazing on the newer ships
Fresh fish at the sundeck grill
Butler escort back on the ship
Pizza delivery service
Cost