Not gonna vote, because my option isn't there.
Physiologically speaking, the development of the brain precludes alcohol into the mid-20's or later. We all know THAT isn't going to happen, and as long as the facts are made available (hello, internet), it's up to people to make their own choices.
Socially speaking, a drinking age that allows parents to monitor and guide their kid's development into a reasonable attitude toward alcohol is preferable. So, say, 16.
This has so many conflicts it's not even funny, not the least of which are access problems (high school being mixed ages) and concurrent milestones (learning to drive).
But: kids are gonna drink if they're gonna drink, and I don't think banning alcohol at high school is any different than banning cigarettes. Legal or no, your behavior can still be regulated when you're on someone else's property and schools haven't really shied away from proscribing undesirable behavior (see: zero tolerance policies).
I'm of the mind that allowing something and not making a big deal of it makes it less of an issue overall. Abstinence-only sex ed is laughable and has pretty damn predictable consequences. My only real worry is that it will push the popular age of illicit consumption down even further (from high school's 14-18 to middle school's 12-15).