Trying AT&T here in the NYC area, and haven't had complaints thus far. I am a Verizon customer (and employee, ironically) but the service is excellent everywhere BUT at my job (where I spend 80% of my time.)
So I purchased an AT&T GoPhone SIM card and got a $60 plan to give it a shot. I get LTE everywhere I've been, and service in underground stations. Looks like I may just be making the switch.