As far as Universal goes, I would say to visit as it's totally different to Orlando, it's only 1 park and the vies are magnificent.
As for Seaworld, "if you've seen one Shamu, you've seent them all!!!!" we went to San Diego in 2002 and it was "ok", went to Orlando last year for an evening and that was enough for us.
Legoland is, IMO, more for younger children which is why we have never visited there (not been to the one in London either..lol).
Love Ella