I have the 14 gallon SS Brewtech Conical, and I'm pretty familiar with the Blichmann Conical. In my opinion SS Brewtech is hands down a better value. Here are a few specific reasons why IMHO:
Fittings: Blichmann uses weldless and SS Brewtech uses sanitary welds. While Blichmann claims this to be an added feature due to the fact you can clean everything. In real life practice, I want to clean as little as possible and prefer the ease of use and flexibility of the triclamp. Plus, SS Brewtech has standard triclamp fittings, Blichmann charges extra for them.
Quality: As always Blichmann's quality is top notch, and in my opinion slightly better than SS Brewtech's, but not to the degree that I think warrants a closer look. I'm generally pleased with the quality of the SS Brewtech. While I don't know if Blichmann is making their conicals in the U.S. like they are their new kettles, expect SS Brewtech to be made in China, but of very sound quality. I also don't know if there is a difference in the gauge of the material their using.
Features: I like that the SS Brewtech can hold pressure, and has a pressure relief valve. I also like that they offer the FTSS, and that is probably one of the things you will need to consider... Do you have refer space for it, or will you need to make other arrangements? I also like that the SS Brewtech takes standard 3/8 casters, since lifting it full can be a bit tough on your back since its sort of awkward to hold a conical and walk with it with 12 gallons of wort. I think you have to buy the Blichmann castors separate, and they are pricey.
All in all, the price difference is obviously going to be your primary driver. Your probably concerned with SS Brewtech's quality vs. the known quantity that is Blichmann's quality. I can tell you first hand that I own a TON of Blichmann equipment, including their new Breweasy, and their quality is second to none. I simply love their products. In fact, I would have loved to have given Blichmann the business if their conical was more cost effective and flexible, but it's just not. It seems like it was great when it was one of the only ones on the market, but SS Brewtech has taken the home-brew conical to the next level.
Look at it this way, you could get an SS Brewtech with butterfly valves from brewers hardware, casters from amazon, and damn near and entire FTSS for the cost of just the Blichmann conical with triclamp fittings. nuff' said...
A photo of my rig for reference sake!
