I have done both with an infant - it really depends on the length of your trip as much as anything.
We are taking our 4 month old in December, and have opted for a condo offsite BUT we will be staying for 14 nights, and we will have a 6 year old with us, so I really felt the extra bedroom would be invaluable.
we took our dd away for 2 weeks in a hotel room when she was 7 months old (it was in Majorca but the setup is the same). We hired a fridge, and a steriliser - I don't know what the guidelines in the USA are, but here we sterilise for 1 year, and it was a real hassle trying to sterilise in a hotel room - although they provided us with a steam steriliser there was no where suitable to plug it in - we ended up with a chair and 2 phone books balanced to get the height to reach the plug! Next time I would pack/buy an extension cable, I don't know why we didn't think of it!
It was also tricky to warm food - yes some food can be served cold, but for 2 weeks I think baby deserves some warm food!
I agree with not heating bottles - we never heated my dd bottles and it was SO much easier - if you have to stop and find a bottle warmer, then that can be a real bind.
I disagree about the buses though - we really like having a car with us, whether we are offsite or on. I find with a stroller it is just lots easier to take the car, and then we walk from the car to the park (unless we are miles back, but we usually find it's not that bad except at MK). I like having the car with us because we carry extra stuff with us (cooler, spare clothes etc), and also it means you don't have to go back to the hotel after each park, you can go from MK, to DTD, to a different resort, to your hotel etc etc, we move around the resort quite a lot and I think this would be harder on the buses.
Bev