It really does depend on where you are going, some hotels are very good at spraying or fogging some not so good. Out of about 10 visits now I've only been very badly bitten once and that was on the Playa Dorada complex and the hotel had a stagnant pond.
Read the hotel reviews, if there is a real mossie problem more than one person is bound to mention it. I would say there are probably less mossies around at that time of year, they seem to get worse about May time.
Another thing to factor in is how good is the protection you use. Being a very tasty person (to mossies anyway

) I have a very strict regime. I've found they are attracted to sweat and that they start to appear as the sun goes down so I stay in the pool so I'm cool till I'm ready to go back for a shower. I use the Avon Skin so soft shower gel then spray with the same oil and then I use the Boots extra strength insect repellent roll on around all my visible sweat points, around the tops of my arms underneath but not right under when your deodorant goes, inside of my elbows, behind my knees and around my ankles as they also seem to like the smell of feet.

This seems to work for me.
I've also got a small battery operated device that makes a noise that keeps them away, it seems to work OK when I'm out on the balcony at night reading but I never leave the door open for them to get inside and spray the room every time I open it after its got dark.
It might seem like a lot of palaver but its become normal to me now I can't cope with the winter without my Caribbean fix.