I use Google more than I use Sprint Nav (Telenav). The Sprint app is also free with my plan on my Epic (The Simply Everything plans include it), although I would have to pay to use it on my Tab. I think the Google app is far more informative, showing in most cases, the exact message I'll see on the signs at my exit.
While I like the features of Google, I wish the voice was easier to understand. This is one feature where the Sprint app is better than Google Nav. I know I can purchase/download other voices, but I'm having problems completing the purchase in the Market...never purchased a paid app until now, and I keep getting an error message.
Combine Sprint's clear voice, and Google's robust (and free) features, and you'll have the perfect app.