go to
http://www.howardforums.com or
http://forums.wirelessadvisor.com/ and ask what others have in your area that works best.
The best way to know is try another cell carrier on a trial basis. If it's better, keep it, otherwise return and move on to the next.
I have Verizon which is CDMA vs Cingular GSM. If I'm not mistaken, CDMA phones will show less bars than GSM phones but will still connect....just the nature of the system, so you can't really compare signal strength by # of bars. I consistently have zero bars at work but still can connect.
Also, if you're on a 1900 Mhz tower, generally it will not work as well indoors as a 800/850 Mhz tower having a longer wavelength which penetrates buildings better.
It wouldn't be wise to recommend which is likely the best carrier for your area, but CAN YOU HEAR ME NOW?
Seriously, test other carriers. The only other option is to use an antenna or repeater.