Which Warframes strip armor the best?
Solution 1:
Well, that's gonna be depending on a few things. You need to remove armor from entire rooms or just the next enemies you're going to hit? An efficient Ash with Seeking Shuriken and some power strength will strip 100% of the armor of something around 2-4 enemies per cast (he throws 2 shuriken and they have punchthrough, accounting for multiple hits). A Mag with the Fracturing crush and some power build can strip 90%+ armor in two casts with decent power strength. The effects are temporary but if you use Polarize once, it should strip the remaining bit, which will also make it permanent. This works even for heavy units at lvl 150, so more than enough for the vast majority of missions.
At the moment, Mag, Oberon, Banshee, Ash, Trinity, Hydroid can remove enemy armor entirely while Frost, Nekros and Vauban can only reduce it. Out of these, we have Oberon, Hydroid, Banshee, Nekros and Frost which can do it on a wide aoe (remove Nekros and Frost if you want complete armor removal). But that may not be enough. If you want Warframes which can remove all armor with one cast, you're down to Banshee for large aoe, or Ash and Trinity.
It's hard to state which is best from this, since each has their own domain.
Oberon requires enemies to be standing on his hollowed ground then using Reckoning 2 or 3 times to completely strip their armor, but it can affect a large area and is permanent so I might rate him as best overall.
Banshee would be best for quick aoe strip. With the Sonic Fracture and some power strength, she can fully strip armor (for 8s, affected by duration) in a (large, depending on power range) cone in front of her. One cast at 145 power strength will strip 100% armor and it's considered a one handed action so you can do it during parkour or while reloading. No setup or multiple casts required and it's a first ability so cheap and easy to spam.
On third I'd place Ash. My reason is, unless enemies levels are in the thousands, you don't need to completely strip armor from everything around you. Ash allows you to focus on whichever target is most threatening and quickly kill them while his Teleport and Bladestorm allows for attacks that ignore armor.
The others I'd rate below because they either take longer (Mag needs to use Crush more the higher the enemy levels, followed by Polarize to remove the last percentage to make the armor strip permanent) or don't offer full control on which enemies gets stripped (Trinity's Links, Hydroid's Corroding Barrage)
Solution 2:
As of Update 20.6, Oberon can strip all armor off of an enemy with 2-3 casts of his 4, Reckoning.