From a California spearfishing perspective - out. Simply no other option. The bubbles that will trickle out of the snorkel during the dive will scare fish away.
When I trained with PFI, they taught us to always spit it out because during blackout the body will reflexively shut off the airway (including closing the mouth) as a defense mechanism. Leaving the snorkel in negated that, and effectively created a straw into the lungs. Also, the recovery breathing on the surface was done with the mouth out of water, not with a snorkel. So why bother leaving it in? The arguments Rick listed on the side of spitting it out aren't even the right ones. If Rick is indeed an instructor, then I guess we could declare that "professional opinion is divided on the subject".
Some people (old people) have always just left it in, and they get stuck in their ways, so they make up all kind of excuses and anecdotal evidence as to why it's acceptable. Terry is a nice guy, but he's not the alpha and the omega. Just because there were less reported incidents of lung complications doesn't prove his point - he's leaving out important variables in the equation. There's been a huge influx of new people into the sport in recent years, and many of them aren't the natural freedivers that he and a lot of the die-hard old timers were. More freedivers, each with a higher average chance for blackouts, and thus more reported incidents of water intrusion. If he could scientifically demonstrate a CORRELATION between water intrusion and snorkel in/out, he'd have a lot more professional support on his side without having to resort to anecdote.