With that name and the comments you can never know if it's trolling or serious but I'll just go with serious... from a PVE perspective:
Conqueror:
DPS (Carnage): Stupid amounts of damage with moderate team support. The highest single target melee damage in the game thus far that I have seen, except for corner cases where a DT might be hitting multiple targets but you are only interested in the one, in which case DT might be ahead. Also a mind numbingly boring style of gameplay where you rotate 3 combos and press just a few cooldowns. No skill.
Tanking (Brute): My favourite class so my bias is out there. Can do strong DPS if played the 'right' way. Aggro is consistent with the other tanks in that some fights are yours, some fights are theirs. Very good against physical, the weakest against magical / protection fights. More complicated than most classes to do right.
Dark Templar:
DPS: In my opinion, why bother with a clown suit (ie: magic damage suit) when you can practically do the same while main tanking.
Tanking (Depravity mostly): Features a Dread Shadow but one of the real, less recognised boons is Vile Zone of Gluttony. A great spec if you are not well geared as it is tougher due to the BYO off-tank and soul barrier. DPS is OP as hell and will make pure DPS classes frustrated. Game play isn't complicated (below).
Tanking (Desecration mostly): Bat **** insane DPS that will make DPS classes wonder why they are there. Sacrifices a little bit of mitigation but due to the outrageous damage they gain a whole lot of life taps in exchange. IMO it is THE spec to run when you are geared. Probaby the highest aggro for the most amounts of situations, and, further, situationally can have some of the most survivability. Gameplay is bland but the DPS numbers are out of this world.
Guardian:
I only have a noob Guardian in blues but have been amazed at both the initial survivability and aggro right out of the gate. It's a class where it's hard to be bad at (there's bad conqs, bad DTs, but there's a lot less bad guards). Friends I have seen play DTs or Conqs very well have commented that their Guardians feel at least as good in aggro as their others.
Biggest issue I see for Guardians is that the other tanks are roughly as capable at tanking as they are but do 5x the damage.