(crusher of foremans cannot be reliably solo tanked by an assassin tank for instance because they suck too much)
I'm a Shadow Tank and I handle Foreman Crusher pretty *********** well. I've tanked all content (still working on TFB HM, my raid group can't skip work/ school like others and one of our guys is in Finland...) and with the exception of DPS and TPS (all tanks can handle and maintain aggro with smart play and DPS that aren't ****tarded ******es) there isn't too much of a real difference between each of the tanking classes in terms of survivability. Sometimes I take more damage than my Guardian Co-tank and sometimes I take less. Same applies to my guild's other group which has a Shadow and Vanguard.
All that said Vanguards/ Power Techs are the easiest to play as and have the highest passive mitigation (and armor for that matter), and the only thing that makes Shadows/ Sins easier to tank with than Guardians/ Juggs is the difference in threat generation.
If you're looking for info on defensives as well:
Power Techs and Vanguards have two (rather weak) defensives
25% reduction in damage for 12 seconds (2 minute CD)
15% health over 10 seconds (3 minute CD)
Assassins and Shadows have three-ish CDs
50% defense chance for 12 seconds (2 minute CD)
100% Force and Tech damage resistance for 5 seconds (1 minute CD, fluxuates)
10% health (2 minute CD, need to be specced for it)
Guardians and Juggernauts have three CDs
50% Defense and 25% reduced Force and Tech damage for 12 seconds (first 3 seconds have 100% defense chance, and this is easily the most powerful defensive in the game, 3 minute cooldown)
+30% Max health for 10 seconds (90 second cooldown)
40% damage reduction for 10 seconds (3 minute cooldown)