We have bad luck with AT&T, but that is our house and we are in a known low cell tower zone. My service also can be poor in cloudy weather. My husband has Verizon for work and his phone works better and can complete calls when I have issues.
However, my phone almost always works- so you might be okay- it depends if it is your sole phone and how important it is. I think I've always been able to make calls, but sometimes it does not go through on the first try. I do have some calls that I don't get (they don't ring and go to voice mail) and there have been times the call didn't register on my phone for several hours (ie, my mom called at 9:30 am and I checked my phone through out the day but didn't get a notice till 2:00 that she called and left a voice mail.)
If you switch, make sure you test it out and see while you are still in the 30 day (or whatever) return period they have so if you do live in a poor spot you can switch back w/o penalty. They have been able to run tests over the phone and check on things (I changed a setting to get my phone to work a little better and there also are signal boosters that you can buy for a home location that has poor reception).
Also, I had a lot of probs this week and called AT&T- turns out they were working on some towers and they reset my phone so hopefully that will help.
AT&T definitely is known to have problems but it really is very specific to the area that you are going to use.