I recently did the following:
Elemental - 2nd try, 933 ilvl. Super easy since ele has insane ST/AOE burst and you just nuke her down. By far the easiest challenge to outgear
Survival - idk like 20ish tries, 930 ilvl. This one was made easier after I got both the class ring and Sephuz, but it's still difficult if you can't aoe the adds down in P2.
Retribution - 934 ilvl, 10ish tries. Only one I've done for Sigryn so far, I thought it pretty hard until I grouped them up and just aoe'd them down without cc'ing her.
Plan on doing enhancement and prot paladin at the least, but maybe will try vengeance and balance druid.