If there is more than one of you, then I would say definitely go with the towncar service.
However, if you are just going solo, then go with the less expensive Mears. Sure, it may take longer, but that late at night you're not wasting any park time, so why not.
Mears only aggravates me when I arrive mid-morning and I'm itching to get to the parks and it takes 3 hours.
Carol