I would suggest the newer hi-efficient models. They are mandatory in most areas these days. I've had a Wood Master since '07 and I love it because of the attributes that come with an OWB. ie,,whole house heat, mess stays outside,,blah, blah,blah.
HOWEVER, my unit is a wood eating hungry monster and you have to be enthusiastic about your wood cutting pursuits to keep one fed.
One guy i know, who has one, swears he gets longer burns from green wood and isn't interested in seasoned wood. Each to his own. I try to stay ahead of the ball and keep plenty of seasoned wood on hand. The un-seasoned wood never worked in my fire place insert and it only makes sense to burn seasoned wood in the OWB. Besides, the smoke from green wood in an OWB would get me run out of town.
With the new regulations here I'm "grandfathered" but will need to raise my stack height before next season.