Been with ATT for 17+ years. Former grandfathered customer on both my wife's and my lines. Moved to NEXT today after much thought. Honestly, I was an idiot because we've only upgraded our iPhones every three years, so as not too loose the ability to upgrade when we were compelled by an iPhone we thought worthy. So that means that for two years over the past six, I've been overpaying for our devices to ATT.
Lower bill. Flexibility to upgrade each year if we want to. No hidden costs or overpaying for devices. Flexibility to bump up my data plan "on an as needed basis" if I think i'm going to be over 30gb (and we've been throttled before). Plus, my wife and I (even with robust traveling schedules) seem to jump from wifi to wifi in our daily lives.
I like that there are more choices now. I'm hoping that I don't regret it later.