They are all very easy imo
I queued with a SCH and a bard this afternoon, we were all noobs, and we got the kill of 4 floors using DF in about 2 hours.
The mechanics are pretty straight forward for anyone who did any coil before nerfs/echos.
Then i did it all again with other DPS friends. And yet another time with a couple other friends.
Things got much worse.
At A1 there was a healer at 95%+ MP all the time, the other healer ran out of MP and me and other tank died.
This happened twice until the bad healer was vote kicked out. One shot after another healer joined in progress.
A2 is one big mess, it's a tank's nightmare if DPS sucks and new adds spawn with previous trash still up, or if healers spam medica2 non-stop for no reason (and yeah i've seen both happening).
As a tank, A3 is by far the best one.
Many mechanics are intended for tanks to handle, which I liked.
Yeah there are some crazy healers/dps that will run away from you when you are trying to get the tether, but if you explain to them they will probably do it properly.
I'm sure if you get 2 tanks from DF who have no clue about anything, this fight will be a terrible experience.
A4 is very enjoyable too, at the very end of the fight (as a tank) you'd better use your strongest cooldowns, cuz there will be mechanics happening all over, big raid damage on everyone, and on top of thatthe boss will do some 5+ hits for 8k+ (unmitigated) EACH.
1st time holmgang saved my ass, got down to 1 HP twice during that holmgang. Second time i had just used inner beast and vengeance just in time and things went much smoother. Third time i was ot so i didn't have to worry too much about it.
For the 2nd leg, when I MT, I never got dragged into the tube thing. As OT, you'll be dragged there all the time, paired with pretty much every other dps at least once.