I started using the thumb over position, then gradually evolved into the aligned along the top position. My biggest problem is pulling back on the trigger, without squeezing it, sort of pulling the stock into the shoulder with the trigger. It's been a bear to stop that crap. I'm doing better, but find myself now and then doing it still.
I don't think there is a "right" way to do it, but what ever works for you, the results should show you the way.
You know, I think my reticence to put my thumb behind the bolt is related to not putting anything behind the slide in a semi-auto handgun. It just feels wrong. Probably why I'm moving into the one o'clock position. You know, just in case the bolt comes flying back...