Difficult... I used to have a Samsung WEP 200 which I loved for the Formfactor
http://dailymobile.se/2007/12/31/unb...tooth-headset/
I think quality wise BT Headsets are a lot better these days, but it always depends on the devices you are using together...
Personally I don't use BT Headsets since I have BT integrated in my car and would always forget to charge the headset, or not have it paired when a call comes in, or or or... just too annoying for me personally.
Plantronics, Jabra and Aliph are generally reliable and get good reviews. Prices should be CONSIDERABLY lower than $150 (I would expect half that for a high-end model).
Ideally start to decide on a formfactor at first (in-ear, loop etc.) and look for reviews then. It might make sense to check out SonyEricsson (related) Forums to look for actual experiences of BT Headsets with your particular phone.