From my experience people in draft pick are generally more competent than in blind. In draft, both teams have reasonable team comps, people generally CS decently, people ward and occasionally remember to contest things like baron etc etc and I usually have rather hard time winning my lane.
In Blind Pick, I get things like Heal+ Clarity anivia, no flash Ashe who doesn't CS etc.
I only play blind pick when I either premade with lower level friend, want to play Kassadin, or just want to trolfstomp (usually ties in with "want to play Kassadin")
Btw, Kassadin has to be the most hilarious champion to play in the entire game.