I think it has a lot to do with what you're trying to do with the reader. If you're just pulling codes, pretty much anything will work. If you're getting into data logging, etc. then there are more differences.
I personally don't have any experience with the OBDII readers... nothing that I own is OBDII that's had a problem, so hopefully others will chime in. I remember seeing a bluetooth plug-in unit that can be used with a smart phone and free app. mentioned somewhere. I think they're pretty cheap on eBay - so that might be an option.