The difference between cabs and limos is that they have different licenses and rules. There is a fixed number of medalions (licenses) for cabs. Not sure if the number of limos is regulated, but by law they are not allowed to pick up fares from the street--only by appointment.

There was a discount outfit that was reliable although their demeanor and cars were a little worn--Carmel--666-6666 in NYC. I used them and they were reliable. Not much more than a cab. Sometimes its nice to have the peace of mind of a car.

Also, a limo is nice when going to Newark because sometimes you have to pay extra since the NY cabbie can't pick up a fare in NJ since he doesn't have a NJ license.