I would like to farm the two lvl 85 areas arachnid lair and stony tomb.

Which build should be the best for this two areas.

FYI: Gear: Full Tal, Spirit, Chances, 2x Nagel, Insight Merc

I was farming arachnid lair with a near-naked sorc and had no issues. If stony tomorrow has zero cold immunes than it's probably just as easy for a blizz sorc. If there's cold immune than you might want to try a hybrid build.

This

Blizz if no immune else hyb

blizzard

fire is great in 2.4

I'm running hydra/orb and are absolutely loving it

Stoney tombs is awesome and super fun, with lots of drops as a benefit!
I did lvl 51-83 there before I even finished a2 and moved to a5 incl. ancients... and by that time I'd found so much stuff that I could finish the game solo whitout any trouble...

After a few weeks I now have pretty great gear, but even in the beginning I could do those tombs as well as bosses really quickly and safe.
Just use TK to open doors from a distance and setup hydras in the room.

Vs bosses simply setup hydras and then tele-orb-tele-orb around them and even your insight merc will survive the encounter.

Using:
20 orb, 1 mastery, no synergy
- and with only 1TK + 1Tele I will have maxed my hydra fully at exactly lvl 99