I don’t do either. I just rotate the piston on the cylinder I’m working on to TDC and there’s zero chance of losing the valve in there. If the valve seal won’t hold the valve in place while you’re compressing it you can run a coat hanger with the end bent 90° roughly 3/8” long into the chamber through the spark plug hole and hold up the valve you’re working on with it. Wouldn’t work with a 2V though, but Really though the seals if fresh(which you should have if you went to the trouble of pulling springs) will hold the valves in place all on their own during the process.
Oh and a tip without using compressed air in the cylinder; sometimes the valve keepers will stick to the spring retainer and push down the valve as you compress the spring. What you do to avoid that is take a brass punch to the edge of the spring retainer before you start, that slight blow will break the bond and the valve seal will sufficiently hold the valve stem in place