Geared, speced and played properly, of course Guardian tanks are viable. They are totally solid.
But you are crazy if you think our PvE utility holds up to the other two tanks.
Pull is so much better than push for trash encounters. Stealth and cc blow away friendly leap (seriously, who uses this!) Don't get me wrong, these abilities are awesome in PvP, but in PvE I seldom if ever use them.
As for leap, storm, speed: they are the gap closers. We all get one, they have pluses and minuses.
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.