I have gone on spring break on several trips over my lifetime and never found it too bad. Like everyone is saying spring break is different everywhere. BUT, we took our dd's last june for the first time in late June and had a BLAST. It was very hot, it rained every day, but it did not hamper our good time AT ALL!
We had such a good time last June that we are going back this summer in August!
I vote June.... But any time in the World is a good time.