Fruit Basket was created by Guy Bianco, a programmer based in North Carolina. To me, it's the easiest site to use because it's mostly hands-off, but still effective at alerting you. While the other options can send you emails, Fruit Basket can alert you as long as you keep the tab open on your browser; the site crawls Apple.com every 30 seconds, so there's less of a chance of you missing an opportunity.
So long as you keep the Fruit Basket tab open on your desktop, you can have it alert you via browser notification as soon as there's AirPods stock available — it'll put a notification in the center of your screen, even if you're on another tab — as well as play a sound. It's extremely effective, especially if you're at work and on a computer most of the day.
This was the site that worked for me: As soon as I got the notification that AirPods were available at Grand Central Terminal, I visited Apple's site, found the pick-up option for that store, purchased the AirPods, and picked them up in person — all in less than 30 minutes.