I've had both and presently use Sprint. I'd say they are comparable, Verizon has better rural service, but Sprint roams on Verizon and other CDMA services, and for $5 a month you can get free roaming so you won't lose anything.
Sprint has made a lot of improvements in the last few years, so anybody that had Sprint 2 or 3 years ago might not have an accurate impression of their current service. Also Sprint has a better easier to use voicemail system imo.

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