I'd say it depends on how you use the car and what your budget is. My bias is for turbos, they'll make more power, get better fuel economy, and you'll never run into belt issues, but they'll put more heat under the hood, cost more, and be more difficult to install.
For a hot street car, I'd probably go with a positive displacement blower due to the mid-range power advantage. If I ever get boosty with my cobra, that's what I'll probably go with due to the aforementioned powerband, ease of install (relatively speaking), and smog legality.
My opinion is that centrifugals split the difference between PD blowers and turbos. You ge the power band of the turbo (though not as much overall power), with the legality, cost, and ease of installation of a blower. If you're going for top-end power, but can't afford turbos, a centrifugal is what I'd suggest.
Mind you, I don't have much experience around boosted cars, and I've never owned one myself. This is just what I've gleaned from talking to other people and what I've read on this site (and others).