I've used Climate Cars a few times and they're great. Mostly on time, their drivers are courteous and well-dressed, and they have a fleet of nice cars (I've mainly been in Prius and hybrid E-class cars).

Every time I get in a black cab, I wish I had booked with them. Most mini-cab firms are atrocious - staff are rude and they have no idea where they're going.

There's already good competition, but if there's more coming then I'm all for it. Black cabs have a bad reputation.

(Edit: no, I don't work for them or have any affiliation.)