The only reason I left Sprint was because of their unreliable text messaging. Other than that, I was pleased with call quality, value, and handset offerings. I know a lot of Sprint technical people, and I've recently learned that Sprint switched SMS providers and which supposedly resolved their SMS issues, so I may eventually give them another shot.
Having said that, the results you posted are a bit of a surprise to me in regards to Sprint. They haven't faired as well in other surveys.