Probably a gasifier from what I understand. Supposed to be the most efficient, but they carry a large price tag. This is a hard one to answer. Ask 10 different owners, and they'll all tell you buy the brand they have. Figure out which have the least complaints, then start sorting from there with your own personal preferences, price, availability in your area, dealer rep, etc, etc, based on your desires. Do you need epa certified in area or will a standard own fit the bill? Central Boiler, Woodmaster, Portage & Main, Empyre all have good reputations to name a few. Wood Doctor & Shaver are two that come to mind that have lots of complaints. My self, I have a Ridgewood, more of a local entity, yet a good product, but I doubt you would want to haul one from Michigan to Montana. Lots of things to consider. Owb's like lots of wood too, better like cutting wood, and being out in the nastiest weather mother nature can throw at you while filling it. These are things I love doing, but some people hate this aspect of them. Hope I helped you a little. good luck on your search!