Eric Fattah's post which sums up it nicely
First of all, if you are on the edge of a blackout, there is NO WAY you would ever manage to 'clear the snorkel via displacement.' That is a technique which requires accurate timing, and an accurate estimate of when you are going to hit the surface. When ascending near a blackout, you have NO IDEA where the surface is, or when you will hit it. Often your last clear thought is at 10-15m deep. There is thus no hope to clear the snorkel by any method if you are close to a blackout.
If you clear the snorkel by blasting, you're finished as well. I have done that and blacked out.
When surfacing near the edge of a blackout, you should never ever stop kicking. Upon reaching the surface you should keep kicking as hard as you can, and tread water with your arms as well. This keeps the blood pressure in your head elevated. I discovered this after years of pushing my limit. If I surface and stop kicking, my vision starts disappearing. If I start kicking the pressure wave instantly hits my head and my vision clears.
The idea that by keeping your snorkel in will allow you to STOP kicking as you surface will just worsen the chance of a blackout...
AND THEN TRUX LAST POST
Rick, you are right that as far as we ignore the safety risks, both ways have their advantages. However, I do not quite understand what "water tight proof" you need to realize that if you black out with a snorkel in the mouth, your chances to survive abruptly drop? Even if there is a laryngospasm at the beginning that prevents the water entering the lungs directly, you probably know that the laryngospasm releases anyway after a while - either when the blackout is too long, or when you wake. In both cases, having water in the mouth will rather likely have fatal consequences. Are you denying that, or are you also one of those thinking he is in perfect control and can never black out?