Quest all the way.
We bought ours for dd when she was about 3.5
She is not a napper, but when we go to Disney we mess a lot with her schedule so she will watch Fantasmic, parades, etc, so she will usually take a nap around 2 pm.
The Quest has bigger wheels and some extra storage.
I don´t know if I will make myself clear, but I was worried that the edge of the seat in the Volo and the Triumph would rub a mark on the back of her thighs, and since the Quest has an extendable foot rest, the seat fabric is folded so it doesn´t rub her legs.
We even used the extended foot rest on the last day of our cruise when we had to be before 6 am for inmigration and dd was curled in her stroller, so with the great recline and the extended foot rest she was really comfy.
I think that the Quest has a deeper seat too, so it makes for a more comfortable seat for an older child.
Would DD ride in a Volo if we had one? I bet she would definetly ride in it if that was the only option, but she is definetly more comfortable in the Quest.
HTH