Another thing, and I may get flamed but it would depend on/off cycle. I am generally a 4-12 rep guy depending on the day, I usually go 4-6/6-8/8-12 and kinda follow an ever changing pattern, I wrote a post here in training about it but no one go interested. Anyhow; as already stated change it up every day and shock your body.
Perhaps myth, but on cycle I hear that hitting some 20-30 sets can really stimulate your body, and with the ability to pump more and harder on test it can actually prove more beneficial then just going to 12. (ON GEAR) Although, there is no science behind this because everybody has different amounts of muscle fibers (Type I/Type IIa/Type IIb) so no one can give you correct information because it is all relative.
The best rep range is the one with consistency in which you WILL do them. Not the amount you CAN do them, lay-mans terms.