Which is best for flinching? Release or classic trigger?

The best for flinching is to know what cause it!! A natural way to fix flinch is to get the book on this site about trigger freeze and flinching.
Release trigger eliminates physically the flinch but not all of them and more than that some people using it flinch big time as well. 
Using a release is like swapping the dust under the carpet. The room is clean but the dust remain there.!

I read the book and there is nothing in that book that is proven to cure
If you start flinching the only thing I  have found that works is first: Change the pull poundage of your pull trigger - if you are flinching you trigger pull is probably 3.00 or less.
Contrary to what you will hear at the club make the weight heavier not lighter.
Go to a minimum 4.0 and if you are still flinch go up .5 pound at time til you quit flinching
You shouldn't have to get above 5.5 pounds before you quit.
Also if your flinching doesn't change with the heavier trigger then you need to check to see if you have a cross-firing issue. Cross-firing can make you flinch - to test simply close your off eye while shooting and see if the flinch goes away-closing the off eye is for the test and not necessary the final answer to flinching