Flat or Up
I would say my tendency over the years has been to take it away flat then lift my arms a lot at the end of the back motion. Start down would be very vertical, and then I would work the shaft back to a more satisfactory plane during the downstroke (this is referring to very old videos).
I think I now get my arms moving upward now at a more even rate, so that I do not have the big lift at the top. I have not had any video work done in a while.
Just trying to get a little better (so I can keep playing well) as I get older - 64 next month - current hdcp is +2 with mediocre putting. Just so I am not 'hiding' anything, I am a former exempt player on the Senior PGA Tour. Just a weekend golfer now - playing for fun, but love the challenge of always wanting to get better.
Bruce