Rule of thumb?
I admit I've been watching way too much TV lately, but it has been the history channel so I claim it's educational.
I noticed that some photographers use their thumb on the shutter release when taking the shot in portraiture. Now for too many years to remember I've used my finger partly as I never considered using my thumb and partly because being a former rifleman there's only one finger for a trigger (we won't go into other fingers for other uses .... don't go there ).
I gave it a try and found that with my QL17 it's comfortable and more stable in the portraiture orientation.
So over to you guys are you a finger or thumb person?