Switched from Sprint to ST (AT&T). So far the wife and I are thrilled with the service. Call quality is better than it was on Sprint. Data speeds are actually better. On Sprint we would only get between 50k-120k on average down/up speeds. Straight talk is either blazing (IMHO) or on-par/better than Sprint. You will see wild fluctuations in speed but so far the lowest download speed was 250-300k down/up, while moments later it will be 5100k/1000-2000 down/up. So keep this in mind.
I spend 85% of the day on WiFi (Work/Home) so it doesn't bother me. Signal strength is much higher than it was on Sprint. Tested GPS the other day heading to work and the GPS lock on the N4 was instant compared to my NS, once the route had loaded it had a lock in 3-4 seconds (Keep in mind we live in a rural area). Porting our numbers from Sprint to ST took minutes on the web. It was about 45 minutes for me, mostly because I had never done it before and was told not to reboot the phone while the port was in progress. After 45 minutes I was kinda impatient and rebooted. Once I did the port was done. So when it came time to activate my wife's it took only about 15 minutes (With reboot).
Now the negatives:
ST customer service sucks. They are very friendly, just expect to be on hold for 20+ minutes just to get to talk to a human. I was kinda stupid and pin locked my SIM but did it the incorrect way and got my SIM PUK locked. Called ST... was on hold for 15 minutes then the system dropped me out. Called back. Hold for 20 minutes, lady told me I needed to call the BYOP number (Which was not listed on the FAQ for PUK locked error). During the transfer got hung up on, called back and another 20 minute wait. But once I spoke to this lady the problem was fixed immediately. So keep these in mind. There is no store to walk into if you are frustrated with phone hold times.
Very happy, would recommend ST if they have coverage in your area and you can live with slight lower speeds. To me the speed is blazing compared to our old Sprint service.
I'm sorry for the book of a post, but I hope this information helps someone.