[3.1] Inferno Sprinkler Knight: Uber Lab - T16 - Shaper - Elder - League Starter (Molten Strike)

What would be good options for mapping? Frost blades? Spectral Throw? I see you use Sunder but I'm not a fan. Would a 3 or 4L Spec Throw work enough to clear trash and use the Magma Orbs for tankier mobs/bosses?

What would be the alternative to sunder? i had another level 91 build using sunder so i would like a different attack skill

Personally I think Spectral Throw could be pretty great. Probably with Tempest Binding for pseudo 6 link, but I'll be honest, I haven't tested it.

Molten Strike itself isn't that terrbile for mapping, but obviously not as fast as Sunder...

I wouldn't recommend Frost Blades, as it doesn't synergize well with Xoph's Blood (if you eventually get it or already have).

Unfortunately, red gems aren't great for clearing in general, apart from Sunder. Maybe Earthquake? Inc AoE instead of Conc, and Fire Penetration instead of Multistrike.

I'm doing 12 hour shifts this week which doesn't leave me a lot of time to playtest stuff, but I can run a few maps tomorrow and see how Earthquake performs. I've noticed that my Shield charge itself sometimes kills monsters on its own (my Brutus is corrupted with 12 lvl WED, where my Shield Charge is), so I could test that as well.
Sorry for not so helpful response :C Maybe I'll have some better answer tomorrow.

PSA: I've have been testing running Blood Rage and upgraded Soul of Arakaali pantheon power last weekend, and I think overall - even with degen - ES leech rate is higher as soon as the Immortal Call triggers, improving sustain a bit more, and dps is also higher thanks to extra attack speed and Frenzies.
I will be testing it a bit more when I have the time with Life/ES/MoM and post my findings, unless someone already tried it - feedback welcome.

Another question: is Witch/Elementalist truly the best class for this? Or anything else viable such as Trickster (more ES)?

Trickster would have a bit more then half the dps of Elementalist. However, 70% increased recovery of ES/Life/Mana make Trickster incredibly tanky, as ES leech is affected by it.
You could roll with Life/ES/MoM version, get Reaper/Shade Form and either Weave or Swift Killer for last 2 points. This will definately increase survivability as your ES leech will be 70% more powerful, as well as mana leech for MoM. You could possibly carry Writhing Jar for emergency "on ignited kill" proc.

Inquisitor - it isn't a crit build, so it ends up straight up worse then Elementalist in terms of dps, and survivability isn't better as well.

Pathfinder - boosts flask charges, but much lower dps. You don't need extra charges if you can dps down any boss in just 2 uses anyway :)

Raider - close in terms of dps, but slightly bit behind. Mapping speed is a lot better, but can die to random reflect monster.

Berserker - around 20-25% more dps. Takes 10% more damage, doesn't have 8% reduced elemental damage. But imo, because of how berserker leech works, you are better off just going full life without ES and get back to 100% life with every single hit.
Life with extra ES buffer works great for characters who cannot always do that, it works like constant 1k regen as long as you attack.

If you don't want to play Elementalist, you could go Trickster for better defense or Berserker for better offense. But in all honesty as a Berserker I'd just stick to any life build.

Best way to level this character?

Absolute best way is picking up Brutus', Thief's Torment, Ngamahu Tiki, Goldrim, Tabula, Deceiver, Lycosidae, Lioneye's Paws/Alberon's, Meginord's Vise and just going left/down/down/right/down/up in the tree.

If you cannot afford Brutus', then you can go with gear less focused on Strength, so Volkuur's instead of Meginord's, Lioneye's instead of Alberon's etc. For weapons:
- go with normal progression, maybe Tempesteous Steel -> Nycta's Lantern/Ornament of the East -> Wasp Nest/Soul Taker/Ichimonji -> Dyadus -> Brutus.
Claws are great for added life gained on hit, which is very strong defensively with Molten Strike.

I've respecced my character to Thief's Torment/Uber Lab farming version (you can find this version in the bottom of the guide). Haven't tried Guardians yet but t15 is still easy and haven't died yet in Lab doing 5-7 key runs every time (out of 25+ Uber Labs I've done with this character so far).

assuming that currency is not a problem (I got xoph's blood) which version would you recommend for farming guardians and shaper between Life and Soul Tether?

In general, Life will be faster and probably safer if you are a good player, Soul Tether + MoM will be slower, but allows you to make more mistakes and can take majority of telegraphed attacks head-on and come out alive.
Before switching into Uber Lab running setup I was testing Soul Tether + MoM more and even though it has lower dps then just Soul Tether without MoM, it is much safer so I'm not sure if this version (Soul Tether without MoM) is worth supporting/recommending. Still, I've done all content with it, not shaming away from hard map mods. Sometimes I died to poor fps/my bad skills but that's different story :)