Question Best humanoid rig.

I'm looking for standardized humanoid rig that will work well with unity and will be compatible with many online resources.

During my searches I have found following options.

Mecanim rig ?
UMA
AdvancedSkeleton
Rapid Rig
Rigify
Mixamo


I do have to say I'm quite green when it comes for rig standards.
I decided to ask for help since decision of selecting rig is very crucial.

 

If I'm not wrong Mecanim-UMA-Mixamo are pretty much same rig in regard to hierarcy etc. Mecanim is not really a rig, it is more like a predefined rig specification, If you use that hierarcy in your rig Unity rewards you with a lot of functions, like IK and re-targetting.
You can turn everything to Mecanim by following its specifications, and turn those rigs' animations to mecanim's animation system and re-target them to new rigs.

Still with some elbow grease and tweaking you can re-target pretty much all animations to all rigs, but it may need a lot of work.

That being said, you can find a lot of commercial and free animations for Mecanim-UMA-Mixamo and you can use animations for them interchangeably but turning them to Mecanim animations. But overall animation quality would be a little low, without any tweaking.

I personally use rigify, becouse it has twist bones (I think mechanim has something like this too but not same) and I can customize it. Rigify is a good tool for animation production and quality but not for compatiblity. I haven't seen any commercial or free animation for rigify. I think this is because rigify not built with re-targeting in mind.