We went with mears last July round trip $28 each. Personally if theres more than 2 of you, go via towncar with quicksilver as its only $65 roundtrip(per car not per person), takes 4 people., you can prebook and prepay from england before you go to.
The only problem with mears is it picks up and drops off at other hotels, so you find yourself doing alot of waiting around, it took us nearly one and a half hours to get to universal, which normally in a car takes 20 minutes!!. Also they never picked us up, so we waited around for more than half an hour, and had to keep phoning them!!!.
Quicksilver have a very good reputation.
Jules