The holidays we've been on:
Haven holidays in a static. DS has been going to this place (Primrose valley) once a year since he was 2. He enjoys it and we could be as busy or relaxed as we want.
Disneyland Paris - this was a bit of a gamble as when the local fair rolls into town DS goes on the same rides in the same order every year (the toddler rides despite being in 9-10 clothes now). He also freaks out when he sees dressed up characters nearby but loves Disney so I decided to risk it and he LOVED it. Went on all rides, even fast/high ones, met his favourite characters for pictures, I really was amazed.
Camping with a tent - DS loves camping as it's usually quiet, he loves the outdoors just pottering about, very low key and relaxed.
The one thing I do every single time we go away though is to print out lots of pictures of the mode of transport, the accommodation, the activities we will do, etc. I get a brochure, we watch clips on youtube, it's marked clearly on the calendar, a LOT or preparation goes into it. We also take home comforts with us... a few of his favourite DVDs if possible, a few toys he likes, a blanket, etc.
I am takng him on my own on a plane to holiday in Tunisia this year so am currently preparing him for that!