You can get a hundred answers to this...what are you looking for? Lightweight? Controlled Round Feed? Dangerous Game? One hole groups? Wide aftermarket support?
For what it's worth, the Remington 700 type actions have the most parts availability and likely make one of the more "practical" customs as fitting things like triggers and stocks is easy and many options are available. But, it's really about what you want in a custom that will drive your choice.
I agree with the above. Lay out some criteria of what you're looking for and maybe people can help point you in the right direction. You looking for an ultralite/titanium, short or long action, integrated recoil lug or picatinny rail.
There are a lot of aftermarket actions that have hit the market recently and they'll have there pluses and minuses.
I recently picked up a Bighorn Origin action, seems very nice, but I haven't had a chance to spin up the barrel in my lathe yet, so I can't give any real world reviwes yet.
A Ford, Chevy, Dodge question.
Which one has the options most fitting for your intended purpose?
Light weight- Ti choices
Versatility- Bighorn and others for interchangible bolt heads
Product history- Defiance, Surgeon Rem 700, Win 70 ect
All of these can make a rifle that will out shoot their owners most any given day.
Price may be an important variable.
The "best" is always subjective.
What are your goals with the build? Cartridge? Weight? Blind magazine, BDL, DBM? Give a few more specifics. Honestly can’t go wrong with many of the choices out there now though.