we try as hard as possible to keep a similar routine to home, and that is what gets dd1 through holidays.
So we go self catering (which I have has a hard time accepting, but it really is easier than trying to find stuff she can eat in restaurants/cafes) and factor in a rest after lunch as her downtime (which she has at home) and so far we have been lucky.
We have been to Centre Parks, Portugal (rented a villa, which was great as nice and rural, had good pool etc), and last year went to California, again self catering.
I have found that if I keep dd1's food and sleep routine the same as at home (so same food - she was having spag bol and curry even in the heat of California last year!) then she is usually quite happy.
We are currently planning this year's holiday - dh wants to go to Australia ! think we've found a good place ot stay (we have to cater for NT teenagers as well as ASD dd1 and toddler dd2) so it's "just" the flight we have to plan!
Have been to Butlins and Haven pre-dd1, and I think they would suit her well on the predictability aspect - they are laces that you can book and go back to, and the rooms are similar, etc. that is the principle we work on now with holidays - most self catering places are similar enough for dd1 to accept.