back wire all the way if available (not back- poke)
have worked with a bunch of kids who think that back wire with clamp is like back stabbing, and wont use the clamps.
its always somewhat entertaining to see them trying to shake the screw out while holding the gfci over thier head while trying to get their wire hook around the screw.....
(there is a reason that the receptacle has holes in the back..... duh..)