The "general rule of thumb" for handspun sock blends is to build a mix of fibers for softness and strength -- merino/finewools for "soft", mohair, medium wools, nylon, tencel, etc. for "strength". I personally tend to rely on a fairly high twist to give strength, and look for ease of care (superwash) or luxuriousness (silk in the blend). But then, the socks are typically for me, and I'm happy to darn them.
My favorite pair of socks to date are a handknit pair from "Little Toes", a 100% superwash merino wool yarn. That said, I've repaired them 8 times now (did I say I _love_ these socks) and finally resorted to using sock yarn (aka a wool/nylon blend sock yarn, Regia I think) rather than more Little Toes, in the hopes of not putting my heel through the sock a third time.
I've been sock-yarn spinning lately, and have examined alot of twist angles of commercial sock yarns -- they seem to use a 30 degree twist angle, pretty "high twist" as my hand spinning goes; the Little Toes was the lowest twist of the bunch, in the mid 20's-ish. (This was the plying twist angle that I measured, FYI.)
So my own sock spinning, 3-plies, comes to about 30 degrees too. I've two pairs to knit now, one from a CVM/Viscose/Silk blend by Crosspatch Creations called "Quinilla in Blue Jeans", and another from superwash Merino in a Crown Mountain Farms colorway called "Hang on Sloopy". _and_ I picked up some superwash Colonial this last weekend at Camp Burton to try out for socks too, as well as some Romney/Silk/superwash Merino from Franquemont Fibers (I think that's what's in it...)
Gee, guess I better get back to my spindles (big grin) and continue the sock-yarn spinning!
(posted by me this day on spindlers)