Verizon
2005, and since 2001 for other people in my family, I have always had service in my hometown of Palo Alto and around the Bay Area, I have great service on the East Coast, and I get great reception on the ski slopes. I have never got a dropped call and very few missed calls.
Prior to that we had Sprint. They sucked. (but I hear there better now)
However, it is starting to bug me how all the cool phones come out first on GSM. I'm eligible for a new cell phone this week, so I'm gonna get another basic flip phone with a vga camera to replace my LG that's beaten to hell and has a shot battery.
Oh, and I agree with ITASOR, I too absolutly hate Verizon as a company. But, as a practical cell phone user who is not an early adopter, the only things I care about are bars, dropped calls, and call quality.