I cruise both lines extensively and find them to be very similar. I am retired, living on a small fixed income, usually travel solo so for me, I don't care what ship, what line or even what itinerary... it's all about the cost.
That said, here's my comparison. I find that the food quality, venues and availability is better on Carnival with the exception of the buffet, which hands down goes to Royal. Decor on Royal is more staid and genteel; on Carnival it can be a bit over the top (but I like that sometimes!). Ship-sponsored activities are similar but Royal gets the prize for self-generated action, with the climbing walls, Flo-Rider, ice skating rink etc. I've only been on ships as big as Voyager class so I'm not as familiar with flying, zip lines, trampolines etc. Carnival's beds are 100X more comfy than Royal's. Staff is very similar, they aim to please and generally do. Shopping is almost identical. Carnival's casinos are slightly better. Royal wins in entertainment and production shows, but Carnival has a nightly comedy show. Carnival wins for kids' programs.
In any event, as someone else mentioned, the passenger base going to Cuba is not going to be the party-hearty college crowd. Which ship are you considering? Three ships are being added this year, right now it's just Paradise. Another Fantasy-class and two larger ships will join the itinerary after March of this year. All are great choices.
Come back and let us know what you decide!