Is this computed over all tiebreaks played in a person's career? Then Federer's can change before he retires and so can't call it best yet. It can change even before the end of the clay season and become less than Sampras's.
However, if anyone has best year round TB stats, I would like to know who holds that.
I have made a few threads about this and also a few very detailed posts in the Federer '06 vs Sampras 96 thread. They include the best years. The players at the top of the list for best year were Federer, Sampras, Lendl, Escude and possibly Borg. I treid searching it to find for you but my search wasn't working. I can tell you that it is fairly near the end of the thread but not VERY recent.