Neither
I use a pair of digital calipers. Similar to the top ones you posted. Also have a set like the bottom ones, but don't use them as much. Probably depends more on how you will use them. I mostly use them to determine the thick of the piece I am turning or to check a plug that comes off the duplicator. In that case, I have the diameters at various locations written down and its an easy check with the digitals.
Jigman