I have the Fitbit One and really like it. I'm on my second after I lost the first one (my own fault, I knew it wasn't secure). Most of my friends have one of the wrist versions but as I have bony, narrow wrists, I don't like to wear that style. I also heard that it doesn't always count steps if you are carrying something and holding your wrists fairly stable as you walk. But then, the One doesn't count steps if you walk softly or smoothly.
I have used the sleep function before but since that involves wearing a wrist strap, I don't bother. I also don't use any of the calorie tracking features, so it's kind of a glorified pedometer.
Trogdor - I briefly used an optical HR wrist monitor a few years ago that was very accurate but I couldn't remember the name of it (possibly an early generation Mio?). That's all it did though, it was not a fitness tracker at all, and I think we had special software to be able to see the HR readout. I did a quick Google search and there are recommendations out there for people who want real time HR readouts for various reasons, so you may have luck with one of those.