Sprint is definitely near the bottom of the CS barrel but unfortunately ATT/Cingular service where I am isn't very good. i'm trying out Sprint with a HTC Mogul and am actually posting this from it.
Nextel is a necessary evil and I have relied on it too. PTT is free nationwide which is nice. It's also very reliable. The speaker mode is annoying as hell. Every so often I would play a little joke when I'd see a group of people with Nextels and I'd do a little chirp and watch them all grab for their phones.