Most of out diving is shallow, no-D, no big deal diving so what we're really worried about is making sure that our SPGs never indicate more gas than you have, we don't much care about the other end of the tail. We do them on a test bench with a calibration test pump and a master gauge.
I still have some of the old Sherwoods and they're pretty good as were the Beuchats. I've never played with the DIR zone SPG, but at over $100 more than I'm used to paying for a gauge they're either great or a fraud.
I can't really speak to the most accurate brand, we tend to buy them 20 or so at a time and they come from the lowest bidder<G>. If they don't meet spec we return 'em and get another batch. Batch seems more important than brand, so I suspect they're all made the same place ... more or less.