I have spent the last few months looking into the efficiency issue, so I wish to share it. There is a comparison in this thread about the Buck versus the BK insert and the Btu's and efficiency ratings.
The guys that produce the brochures are all the same...mostly. When the manufacturers test the stoves in the EPA approved labs they get all sorts of data or test results. More often than not, they only burn test fuel and not what we burn in our stoves...cordwood.
The results they get are NOT in any manner what we get in home usage. During their tests (again on test fuel) they may see a spike of 47,000 Btu's...so they take that number and use it in the brochures! Watch for wording such as "Up to" or "As High As". These should raise the red flag. I notice BK uses both the results from tests and what they call "Real World".
As for efficiency, in order to get all their stoves qualified for the 2009-2010 tax credit, they used a method called Lower Heating Value. Hell, the number is vastly better than the number they had on the brochures in 2008 for the exact same stove

If I understand it correctly, and I have been wrong plenty of times just ask my wife, the Lower Heating Value efficiency excludes the weight of the fuel load that was water. So if they put 40 pounds of wood at 20% mositure content, they exclude from the calculation 8lbs of fuel (as water).
I don't get to do that in my stove! So I much prefer to see the efficiency number that is the average from their prior to tax credit BS calculations. Look for the overall efficiency and according to a friend, he says it was called the higher heating value. Almost always the higher heating value is much lower than the lower heating value. So when you look at brochures and speak with the dealer, make certain they are showing you apples to apples comparisons.
Also, I hear Buck stoves are pretty bullet proof, just like my Blaze King. Go with your gut and buy the one that makes you happy!! (And your wife happy or you'll be sorry!)