Juggs have the best CD's for tanking. Your friendly leap reduces dmg taken by 20%, you should be useing it on stuff like the person who gets targeted with the lasers on TFB Kephass.
Juggs are the hardest tank to play, yet, the most rewarding. They have the best overall mitigation and CD's of any of the classes.
My understanding was that assassins have those things you just said (best CDs, hardest, but best when played well). Do you have evidence favoring juggs?