Frost Mage.
Get lucky enough with the powers then the last boss is dead in anywhere from 5-10 seconds and that’s on layer 3. I have seen a video of a 1shot but not been that lucky (if you can even do that now)
Holy priest by far. You breeze through, can pull many packs at a time and AoE them down, has amazing Anima powers. Shadow is very slow at times and can’t pull a lot all at once.
On retail, I’ve done Torghast as Resto druid, as Feral, as Guardian, and as Vengeance DH. Of these, VDH is by far the most fun (but at the moment, resto druid is faster, thanks stealth): there are some very fun, and very strong powers to be had in Torghast. If I can stack sigil cooldown reduction and decree damage increase, the run becomes a decree spam fest, and that’s mind blowing. Literally. Things just blow up, all the time.
Infernal Strike has some nice powers too: increased range, increased damage, and runspeed after a strike. There’s also a very, very fun one: 1.5s CD on it for the next 1.5 minutes after taking the power. Combine that with increased damage, range, and runspeed, sugar it with increased decree damage, and you have a DH that pulls the entire floor in about 15 seconds and decrees and jumps them down in another 15 seconds.
Fire and traps in the way? No problem. I jump over them. Elites I want to skip? Jump over them, sigil of chains behind, shadowmeld.
So. Much. Fun.
On Beta, I cleared Torghast with every healer too, and disc was fun too. Can’t wait to have my disc alt ding 60, so I can have a go at it on live too. I doubt it’d surpass the fun I had on VDH, though.