Price, looks, flames, clean glass to see the flames, money back satisfaction guarantee, Cheap parts, cheap cats, color choices, custom colors, custom designs (IS), renowned customer service, top-rear vent reversible (except FV), soapstone feel (have to experience to appreciate), no middle man, no middle man obstacle if customer support is needed (kudos to BKVP's presence here), max BTU/hr output, left-right-front load options, ash pan system that Works, andirons, adjustable height (IS).
BK's have their advantage (thermostat) and offer an awesome stove. If I had to change brands I'd buy one. I need a very low output (long burn times) stove due to climate and insulation. I manage this 95% of the time with two 1.3 cuft loads (often partial) per 24 hours in a Keystone. Usually a 14 hour burn and a 10 hour burn per day. Yes a 2.85 cuft Princess would manage this, and would be my second choice. Some people need lots of heat, some need long burn times (the King does both well at 4.32 cuft).
Oh good, somebody took the time to list some strong points of the IS.
1) Price, not a point for either. The IS is the same price as the BK once you include shipping.
2) Looks, subjective of course but I too have called the BK ugly. It grows on you. The WS stoves are often deemed too artsy. So no points.
3) clean glass, When you burn them hot the folks say that their BKs stay clean but on low my BK window doesn't stay clean. Perhaps if the IS could be run at low temps then it would dirty up too. Hard to say. I wish my glass would stay clean on low. Point WS but only half.
4) money back guarantee. I always thought this was to make up for the fact that you couldn't see one at a dealership. I have never wished for a money back guarantee on any of my stoves. It is unique to WS so if that's important to you for some reason then there you go. If it was good you wouldn't need to return it. Half point WS.
5) Cheap parts and cats. This slight advantage is present but very small and hardly of value. I worry more that you need parts. 1/4 point WS
6) colors. If it's really important, anybody can spraypaint any stove. Can I guess that 99% of stoves are black? 1/4 point WS
7) artsy design cutouts at extra cost. To me they are unattractive but they are optional and some folks like the art on their stoves. 1/4 point WS
8) Customer service, never been lacking from my BK or hearthstone for me. Always had direct communication with the manufacturer or dealer. No points.
9) top or rear vent, for sure, this is a point for IS if you need it. one point WS.
10) Soapstone feel. Completely unimportant. I've had a stone stove and this is all hype. No points.
11) No middle man. Funny, in this case the middle man can only help. You certainly aren't paying extra for it. Seems the WS would wish they had a middle man to handle shipping or loading into your truck. point BK.
12) Higher max btu out, point WS. Not sure I believe it but it is rated higher.
13) Left right door options, this is another option like #6 and 7. Woodstock offers options on the IS. THis particular option gains 1/4 point. Together they all add up to a solid point.
14) ash pan. This is interesting. I've never used a good ash pan. I have been using the BK ash plug system and it works but how to rate this. Is it really of value? Benefit of the doubt, point for WS.
15) andirons. Not valuable, more harm then good. This is an art option covered above. No points.
16) Adjustable height. No value to most. No points.
1) thermostat on BK, point BK.
2) double the burn time if you want it, two points BK.
3) Dealership network, you can go see one, people know what they are, high market share, point BK
4) deep ash belly, I've emptied ashes twice all year, with the ash pan system. The deep belly keeps sparks, logs, junk, in the stove. Point BK.
5) BKVP on this site to help, no WS representation, half point BK.
6) Blowers and convection plus radiation from front. I didn't think they would matter but they make a huge difference, especially in a basement application. half point BK.
7) Spark protection hearth pad only on BK, IS requires R-0.41, half point BK.
You might not agree with my point awards but what we are trying to accomplish is a list of comparative pros and cons that you might assign your own value to so that you can determine which stove is best for you.
I would be happy to own as IS, especially out in the barn where I could really use that high top end output.