In principle clever sledging (Let's ignore the Clarke example) is fine from anyone. All I'm saying is that in my opinion sledging has to be backed up with something, otherwise you end up looking like a bit of a tit.
As most sledging is done early in someone's innings how do you know who who is crap and who is good?? And you can't exactly know that you'll get run/wickets. So by that only the odd bowler first innings can sledge and maybe one or two bats in the second ? (Assuming you need to score 50+ or take 3/4+ wickets)
OR
Just shut up and play cricket and leave the other team alone as you are irrelevant to them as they are to you
then everyone is happier as they is no utter rubbish spoken