I've had both Time Warner and AT&T, currently AT&T. I was MUCH happier with Time Warner, but have been giving AT&T the benefit of the doubt since my package with them is considerably cheaper (about $35-40/month less). They've got one more strike before I call to cancel and switch back to Time Warner.
AT&T's reliability is subpar and when my DSL goes out, I have to spend at least 1.5hrs on the phone for some answers since the first 5 people I speak with have no idea what they are talking about. I've called probably 5 times during the half year I've had AT&T and, to their credit, they will get me straightened around, but it takes a LONG time (I'm no computer programmer, but I'm far from illiterate). We were without TV for a full week (not a huge deal, but certainly an inconvenience) when my wife simply unplugged one cable and reconnected seconds later to move the satellite box.
The rep who came to fix it said never to move or touch anything. That's inconvenient.
Also, we've got two stupid satellites at our house because the old one wasn't up to snuff and they refuse to take their junk from your house.
The last time I called when my DSL password was randomly reset, the first 2 people I spoke with didn't know what OSX was. I had to spend 2 good minutes explaining that not all computer ran Windows.