To be honest, I had more problems with an AT&T landline than I've ever had with VOIP.
At least with VOIP, you don't have to rely on some dude in a bucket truck come and check your wiring when things go wrong.
911 with VOIP almost always goes to the same center as landlines, and the one time I had to call 911 on my AT&T line, I had to be transferred twice, so I'm not sure VOIP would be any worse.