I'd lean towards April, especially if it is a shorter vacation (<10 days). February can be very nice but a higher risk of wet/cooler weather and missing dives due to a Norte. We usually head down 2-3 times a year for about 2 weeks each trip. We don't mind missing 1-2 days diving but if other travelers (especially non-divers) are going with us that have limited travel time we always take them in April/May. The weather is 'usually' more predictable, yes it is hotter and not nearly as many Eagle Rays but less crowds and feels more laid-back (less cruise ships).
That being said the Carnival thing (in Feb) makes for a great trip. One year we did a family trip that spanned 4 generations with divers, non-divers, partiers and old farts and we all had a great time with fantastic weather. The next year most of us went back to repeat the Carnival experience and the weather wasn't very good for an entire week. Didn't bother the divers but the beach bum folks in our group weren't very happy.