Worst.
Twice we called for a Yellow Cab, one never showing up, and another asking where we were going and telling us they weren't going that way. When we actually did take a Yellow Cab from our hotel, the cab driver was drunk, forgetting to turn on his headlights (we told him they weren't on), and he hadn't put on his seatbelt. This was after 10 minutes the warning beep had been going off and each of us (4 passengers) determined we had our seatbelt on. After he noticed it was him without his seatbelt on he just turned to look at us with a crooked smile and mumbled something.
Definitely take either Uber X, Red Cab with Tony Macaroni, or the cabby with dreadlocks playing great 70s sexy music.