The Sennheiser headsets work well and are more durable than they look. I have used the 25KA series in the ATR, RJ and a pretty wide assortment of General Aviation aircraft. They do not have much passive noise reduction (11db) but it is enough to operate in the RJ without having them even turned on. In GA aircraft I usually don't flip them on until after the climb check because so much noise is cnx that it is difficult to hear anything abnormal during the run up.
With the ANR and the ear cup design, I think the Sennheisers do a little better at reducing noise than the 850's I borrowed to evaluate. But the 850's are slightly more comfortable.
Some turboprops are louder than others. The ATR was pretty quiet and most of the noise is in the lower frequency ranges. Apparently the extra work the headsets do in these frequencies shortens battery life considerably. In the RJ the batteries (when in use) last several weeks to a month. In the ATR you were looking for another set after two, or three, days. You will want good rechargeable AA's, anything over 2100 MAH will work.
For a good price try these guys:
http://www.aviation-headset.com/
They get trade show demos that look and work like new. I've referred several friends and family members to this place and every headset has looked like new (in fact we suspect they were never pulled out of the box before).
Also be aware that the KA and the KAS series both come with stereo plugs. Some of the turboprops need a 1/4 inch adapter from mono to stereo to work with the Sennheisers. These plugs are available at Radio Shack, Best Buy, etc..., for less than $2.00.