i agree with willyp
i do BB with alternating grip like you would with deadlift. i throw on six a side and some change, straps if needed, and bang out some good reps. the grip doesnt change the development, but as willyp said DB can fix that if needed
SO:
BB Shrugs: Heavy x 2 sets of 6-8
DB Shrugs: 120 x 8, x8
on BB i go for heavy overload, i dont care about perfect form, etc
on DB i go for slow power up, squeeze and controlled down with a big stretch at the bottom
for me what gibson said with the 5 sets is way too much
i usually would do two heavy BB and one nice and easy DB, but always going heavy as possible
oh but also the heavy shrugs can be hard on the joints, be careful and even if you can jump 40lbs in a week, relax and take it slow. within two months i went from 315 to well over 500 and although my traps blew up my collar bone joint was not to happy...