All depends on the type of tickets you want.
For example UK Ultimate tix are not available out there so you have to buy in UK but if you wanted a 1 day Disney ticket its cheaper at the gate than anywhere else.
7 day MYW ticket would cost $300.75, it says $5 off gate price. Personally I would just buy at the gate, $5 is not worth buying elsewhere to me.
It works out at £190.71(£193.88 at gate) using a fee free credit card.
UK tickets for 7 days(get 14 for same price) are £249ish, incl water parks, hop, Disney quest and now minigolf.
If you don't want all the extras then the US MYW looks better value