The best pack, whether it be draw string, classic padded, or even messenger, is one with just one pocket (Think grocery bag).
Size and type don't really matter, but the more pockets, the longer you're going to be in line as they go through them all (including sunglass cases).
I don't think any ride requires you to remove your pack, maybe stow it under the seat (like Star Tours).
When I went, I used the Under Armor Exeter sackpack. I found it pretty comfortable but it isn't that way for everyone. My objectives with the bag were big enough to carry a light load out (water bottle, backup battery for phone, snacks, sunscreen, sunglasses case, and hand wipes), but it wouldn't trap heat against my body. I thought the Exeter sackpack suited the purpose perfectly. I do wish it had less pockets, but given that I never stored anything in there, it didn't slow down my security check all that much.
It might require a little trial-and-error to find the right thing for you. I know I went on many hikes with several different types before settling on the sackpack. One of the other tips (found here) is to organize all your small stuff into ziplock bags.