I would wait to see what the reviews are like for
Legoland when the weather gets hot. You don't mention the ages of the folks in your party, but there are challenges at legoland for large families or single adults traveling with kids under 48".
I think it will be interesting to see how the park is precieved when the weather gets hot. There are very few places to get out of the heat. Most of the attractions are outside. Some of the lines have some shade but in the humid hot summer that shade tarp isn't going to be too helpful.
My kids spent a lot of time in the playground areas, and in the heat those will be miserable at best and dangerous at worst. The wisdom of arrive early and then leave and tour late isn't going to be overly helpful even if they extend hours to 9-7. They are opening a water park this spring so that might help.
We really like busch gardens, and if I had to choose between BG and LL, BG would win hands down every time.
I'm not really sure why, but I just really like BG. My 2 and 4 year old had a great time at LL but it was a lot of work for be because of the height and age restrictions. There is no way I would pay full price. Now the 2 day deal isn't bad but the one day price is steep for what is offered.