Honestly I use any at-level slag weapon with a high fire rate. This normally means Vladof (pistols or assault rifles) or Tediore SMGs.
I’m currently level 61, running a hybrid.
First spray down the enemies with your slag weapon
Second enter Decepti0n
Third throw your kunai
Fourth switch to your preferred damage dealing weapon (melee or gun)
An optional step to the above sequence is throwing your grenade, depending on your play style and gear. I.e., using a singularity grenade to pull enemies into your decoy for Unforseen.
I like to save my grenades for other purposes than slagging, like stripping shields or singularities.
A slag Rubi is obviously nice for melee or hybrid, but not everyone has one. Plus the slower fire rate on a Rubi only makes it effective for slagging one enemy at a time.