If it's itinerary you're deciding on, then I'd go with the Legend. I'd prefer Grand Cayman over Costa Maya, even if CG is a tender port. The rest of the itinerary is the same, so I guess you should also look at the amount of time spent in the remaining ports and which one is more condusive to your plans (e.g., prefer early arrival/departure or late).
I am not sailing the Legend in April, but I was on the Dream in June and LOVED it. I'm actually a little apprehensive about the Legend now, because it doesn't have the seaside theater, mongolian wok, burrito bar, or smoke-free spa cabins. Still, the price was much cheaper for the Legend than the Dream, and the Legend will seem less crowded since it is smaller.
Also, many people prefer the layout of the Spirit class ships.
Prioritize what matters most to you, and then decide. Here are my votes for the various factors:
Price - Legend
Itinerary - Legend
Ship ammenities - Dream
Embarkation Port - Dream (Port Canaveral is my fave and closer to me)
Layout - Dream (for me, but most would choose Legend)
It's your call, but I think you'll have a great time no matter which ship you choose!