All ball valves are not the same. I saw some 3/4" that were about 1/2" on the inside. maybe thats why it was cheaper. You need to look and compare.
I would think a ball valve would allow you to "fine tune" the air flow better.
If I had the extra cash at the time of purchase, I think I would buy 1" valves for the extra flow.
Yeah I noticed that too while looking at Lowes today that the actual hole through the center was not that big. Definately not 3/4" of course that refers to thread size not flow. The 3/4" PVC had much bigger hole for flow. I guess with the low temps you could use PVC valves especially if a riser pipe is used for intake.
ROLL TIDE! UDS as of 12/2/11, Chargriller w/sidefirebox, 2nd UDS in the works