This is my current End Game Meta build.

::Updates:: Recently updated with some notes and to be current with the meta, although I left the original information for posterity and notated the reason for changes in one section at the bottom.

Some notes: [Flow] is flexible between [Vigorous Swap], [Augur Secrets], [Constitution], and [Fleeting Expertise] depending on how you want to structure the balance of your kit. [Streamline] is much the same but I don't recommend replacing it with anything but [Fleeting Expertise]. You lose some range on pillage and some duration on 2 and 3 but the tradeoff might be worth the better energy management to some. (small update note: it is worth in high level stuff, more below)

[Brief Respite] means pillage can give you shields at the beginning(::U:: 1) and end of the cast effective being the spammable "take their armor and make me not die" button. For any high level content involving armor in any form this build feels better than anything else. [Rolling Guard] gives you a quick 'oh snap' button. Personally I prefer this variant with the higher duration because I don't have to spam my buffs all the time and the range on pillage is nice. (::U:: 2)

Archon crystals are players choice. I recommend 3 power strength and 2 cast speed if you want a nice balance. You can also take 5 strength though and be totally fine. I do NOT recommend secondary crit chance. There are math reasons involved but it boils down to 6% chance for orange crits does not equal the same benefit you get from 30-75% strength depending on if you got Tau crystals or not. Across the board strength just feels more worth it. (::U:: 3 *min maxing advice)

End of the day I am pretty supportive of play style and what feels good to how you play > mathematically "perfect" build. If you are looking for a well rounded build that feels great in endgame with a forma loadout that has nice options though, I highly recommend this build.

Now, why the Archon mod varients? Well it's mostly for regulator loadout options but I use Galvonized Shot and a toxin/radiation build almost exclusively these days. The damage against corpus is second to none. Radiation hurts infested aura sharing which makes it good into that, despite a dps reduction from resistance. And grineer without armor suffer greatly from toxin DoT and have no resistance to either type. With armor, radiation gets a damage bonus. It works well all around. Toxin procs will also proc corrosive which is 2 status effects for the price of 1 thus doubling the damage from Galvonized Shot. (::U:: 4)

Regulator build can be found on my profile here.
Updates:
1) No longer worth due to shield gating changes, still gives armor at end for gating. [Brief Respite] is basically useless and [Growing Power] takes the spotlight for additional stripping power on pillage as well as more damage on [Regulators] as power strength scales more exponentially on them due to the amount of multipliers it affects.

2) higher duration with lower eff gave way to energy droughts at times and can make endurance runs harder during times of high pillage spam for survival or armor stripping, especially at high level circuit content. Simply put, [Fleeting Expertise] > [Streamline]

3) When speaking on Tau archons for min maxing, 2 orange for crit, 2 red for strength, and 1 yellow for cast speed is probably optimal. This affords you a 150% crit chance boost which places you in orange crit town, 30% str which allows for modless shatter shield cap if you wanted to make a more defensively focused build, and cast speed which helps in just about every way for fluidity and response time. If you don't have tau, the original advice still applies, non tau orange is only worth if you take 3 and that's not worth the extra slot use or the loss of non tau orange and yellow in my opinion.

4) Nothing about this has changed, although I will note that upfront damage will be lacking compared to other builds unless you are in the circuit and get extra damage/status stuff. Status application is relatively weak on [Regulators] but I still like [Galvanized Shot] to take advantage of status procs from other sources or using a primer build [Epitaph] to prime a group of enemies and mow them down nicely. Synergizes well with the status build Dual Toxocyst as well. The damage types for rad/tox is still my go to. Radiation is too op for high level content where eximus aura stacking can become painful if left unchecked. Toxin for bypassing Corpus shields is damn near required at high level play. Their shield HP gets a little out of hand. It just works well.