Glasgow, Scotland to Shannon/Ennis, Ireland

Well, "best, fastest" is usually private helicopter and private jet -- if it's good enough for Presidents and Popes, it can't be too awful. The pricetag is pretty high, though, so it helps if someone else is paying.

If someone else isn't footing the bill, you're probably going to need to make some choices along the old costs-versus-other-considerations axis.

If you fly, there are no nonstops between Glasgow and Shannon. One-stop flights would go well out of the way, with a stop in London or other airport in England. Shortest option would probably cost about $500.

If you switch your departure from Glasgow to Edinburgh, then Ryanair flies nonstop EDI-SNN (most days a week, but not daily), takes a little over and hour, and it's cheap (US$60 for starters). But it's Ryanair...

That private jet probably would be a lot more fun though.

Ha, you sold me, David! Now to find someone to pay for it!