Last one does look better,What helps me help others is tell them to slow ot down,when you do slower reps its near impossible to cheat,then you'll get the feel for proper form and can get things moving fast like they should,up as fast as you can w/o cheating(momentum)anddown slow,if it takes one second up,2 seconds down...good starting point,pretty much if you feel a good burn your not doing it too wrong,Arnold was a good example of a Proper way to cheat,he would do his reps then as he ebgin ti fail he would increase the momentum to get those extra few reps,like having a spotter on bench,similiar anyways..forced reps are great...I like my DB curls standing,so you can lean into the curl a litle more than seated,seated I like one arm Isolation DB curls,you can spot yourself that way and get a few extra forced reps at the end,really burn em out'