I've only tried ABC once, but they did three things that Ace Taxi (by its many names) has never yet done for me: a) they showed up exactly when they said, b) they charged what they said they'd charge and c) they took a credit card without a problem. (But note: no Discover.)
They gave me an impression of being smaller and less "advanced" than Ace. (No automatic text alerts; credit card taken on paper, not a swipe machine.) But even so, they did the job more efficiently than I am used to, and they arrived exactly on time in spite of bad winter weather. The driver even called twice: once an hour before my scheduled pickup to make sure he knew how to find me, and again five minutes before. That's being organized, even without the on-board tech. (They did have a GPS to get around, of course.) Ace sends a text saying a cab has been dispatched... Neat! Except when no cab arrives.
I'll use ABC again, and fingers are crossed that this good experience was not a fluke.