We used Happy Limo last September and there wasn't a thing wrong with their service.
We were staying at the Poly and they had a driver waiting, ready and willing to help with luggage, when we arrived at the baggage carasoul(sp?).
Their prices were competitive, they had a grocery stop, and the drivers were very nice.
One advantage on the grocery stop, you could fax your order before you even arrived and the store, Albertsons(?), would have it ready. Pick-up, pay, and leave. Probably 10 minutes tops. That's pretty nice when you're excited to get to your resort.
We even rented a double stroller from them. At $25, and we were there for 8 days, we saved a few bucks over the Disney rental.
The tip is supposed to be included in the price, but the drivers were so nice I tipped them personally. They were really nice to our girls, ages 3 and 4.
It sure beats Mears. If there is any way, I will never use Mears again. We've used them on two or three other trips and you feel like they're just herding cattle.
The town car or limo is the way to go.