Just finished another nice stay at the Regal. Convenience cannot be matched, our room was perfectly fine for an overnight, and if your stay timing allows for breakfast - then booking an executive club room is worth it. The omelette station is a nice touch, too.
As for upgrades, I’m LT Titanium at Marriott, but would still choose the Regal anytime. I can’t speak to other Regal properties, but HKG is fine.
Good luck
Dave