What cell phone service should I switch to from AT&T (in NYC)?

My cell phone service, through AT&T, is terrible. (I’m in Manhattan, but it was also like this in upstate New York.) Any given conversation is likely to get cut off, and the reception in my office is really bad. (My office is on the 2nd floor of a skyscraper.) Sometimes the person I’m calling can’t hear me even though I can hear them.

I have the impression Verizon gives the best service, but I would probably want to get their unlimited plan, which would be $90 a month (as opposed to the $55 I’m paying now). Does anyone use anything that’s more affordable but with decent service in Manhattan?