General rule of thumb is 1.5x your truck's weight AT MINIMUM. Given 6000# for a Blazer, 9K is minimum. More if it's going uphill, if one or more tires are stuck past the axle, etc etc.
If you're patient, you can find a deal on an 8274 or similar older winch. Rebuild it yourself and you spend the same money you would on one of those Chinese cheapos... and you have a winch that'll run all day and pull your butt out of a jam. (Or, as mentioned, the other guy =))
My 20-year old Ramsey is rated for 8000# single-pull and like the 8274's is prolly grossly UNDER-rated. It cost me just over three bills, including a rebuild to keep it going another 20 years. I've got a helluva lot more peace of mind than I'd have with a cheapo.
Anyway, search on winches and you'll find a bazillion threads where this has been beaten to death. Some people insist on buying cheap, some people insist on buying quality.
Also read up on recovery
http://www.pirate4x4.com/tech/billavista/Recovery/
And make your own mind up after that.
-- A