Depends on the bass. The best acoustic bass I've ever heard was a fretless pre-Fender Thunderbass. I wouldn't say it "nailed" that upright tone, but it had a beautiful, airy quality, and the lack of frets made it far more expressive than the fretted models. But I really guess it all depends on what kind of sound you're going for.
Hi. My name is Sean. Now you know.