I did the Dolphins in Depth program in the Spring of 2000 and LOVED IT. It was awesome! Your dolphin encounter is only at the end of the program...you spend a good portion of the morning getting a backstage tour of the Living Seas pavilion. I don't know how it compares to Trainer for a Day (where is this?). I think Discovery Cove gives you significantly more time with a dolphin, but it also costs a much more $$$. DC was out of our budget, so Dolphins in Depth was a perfect fit.
This link to AllEarsNet.com has a description of Dolphins in Depth, plus some user reviews of the program (and other backstage tours). The reviews give some nice details about all the tours.