Normally I would say bigger is better, but that 30" front to back depth may make it tough to reach the bottom/back of the tank especially in the center. It may seem stupid, but I would suggest mocking up the dimensions with cardboard or something you have around the house to get an idea of the "real" size of both tanks. I think this will help you determine how comfortable you will be working in the tank.
As others have said, if you have quality lights, the depth shouldn't be an issue.