BlenRig DOES focus on mesh deform but you can just as well weight paint it like any other armature.
I must say though, Blenrig includes some extra bones and the controls just really feel much better to use, plus it includes some auto/premade movements to make the joint movement more natural, I very much prefer it over Rigify/Pitchipoy but that’s a personal preference, so it’s best to try both/3 and see which works for your characters.
Rigify
The actual difference is that Rigify is customizable, meaning you could build a person with two arms just as easily as one with 6 arms, a cat or a spider; BlenRIg on the otherhand can only make a two arm-two leg human with a face and you’ll have to manually add/remove bones and create their controls yourself, Rigify on the otherhand automates that.
You can also use Pitchipoy if you want a human face for a Rigify rig.
Rigify also operates on the principle that once a rig is created, that rig should no longer need Rigify. This means you can always distribute rigs created with Rigify to people who do not have it and the rigs will still function completely.
Meta-rig are like joint heirarchy templates where it contains the position of joints for rebuild.
deformation bones are in layer 29.
Rig Anything with Rigify Tutorial Series
Autorig Pro
Has that nifty automatic finger rigging placement.