Which of these should I 6-star first?

Solution 1:

With decent runes, Susano can become an amazing Faimon farmer. I would go down this route because the energy return on this scenario is a lot better than say, Tamor Desert North(3)

My Baretta can farm Tamor Desert North (Hell) if you're on Global, feel free to add me (efcseany21)

Lapis is good with Revenge runes for the newer Necropolis Dungeon, however - with this being your first 6*, I can't really imagine you trying to progress within this update. While Sath is a good choice with his two AoE attacks, also for Faimon Hell (1). Vigor is also a good unit but requires 6* energy runes (spd/hp%/hp%) with his Shred and Predator's Cry skill maxed out to be effective.

I hope this helps.

Solution 2:

I understand this question is very old, but I'd like to add an extra perspective on what to 6* first in Summoner's War.

Almost any 6* can solo hell stages in the first four regions of the game, at a minimum, but a farmer designed to farm somewhere like Faimon hell is going to be relative trash if he has poor runes.

At this point, with the new tutorials on advancement, just giving Lapis the vampire/revenge quest reward set is enough for her to farm Faimon hell at max 5* (after you +12 the even runes and +9 the rest).

Either way, your initial focus should be your giants team, as Giants B10 will make or break your progression. This team will get you the runes you need to make a faster farmer. Any unit that either needs a lot of different stats to bring out their best (such as Belladeon) or is designed to be a major damage dealer (such as Sigmarus/Veromos, if fused) are good choices, but opt for survivability first and extra damage later for faster clears.

Once you are clearing Giants B10 in about 2:30 per run or faster, you'll be getting the runes you need to build a dedicated farmer for speed farming XP.