I'm 42 and no children and have been on Royal Caribbean, p&0, NCL, princess , MSC in yacht club and marella. I've done 8 cruises so far and 9 and 10 booked for this year m.
I'd not go in marella again but would do all the others. I'd also try celebrity Depends on itinerary, price and drinks packages and so on. All biggish ships with pe the to do. Mostly adults groups with a few family groups.
There are pros and cons of all cruises and ships.
I'd go for a ship built in the last few years, say since 2015.
Som benefits:
P & 0 go from Southampton
Princess and NCL have good value packages
Princess and celebrity are premium luxury
Rci and NCL are resort cruises
PO have a distinctive British slant.
MSC is very European and busy but we did yacht club twice which is divine and if you get a good deal with it
PO do single rooms on their bigger newer ships Britannia, Iona and arvia
Princess is a bit stuffier and older clientele but I loved the food and service and ship.
NCL was great for me the service was exquisite, lots of adults and a fun vibe a beautiful ship and spa which we had a access to ans fabulous itinerary.
All Food is included in but you can pay for specialty dining. Food varies on cruises. I liked princess food the best. NCL buffet was amazing. Marella was truly dismal. Drinks are extras unless you buy a package or it's all inclusive like yacht club and marella m.
Beware British based you tube reviews because they are not impartial. They are paid or paid in kind to give reviews.
Cruise nation do good packages cruise kings offer a better service. If you get a few ideas I can explain a few.