Which rum is best from the popular ones you can pick up at airport duty-free stores? Bacardi, Myers, Captain Morgan?

XM Royal is my favorite rum, it's from Guyana and very tasty ^

Just my opinion, but I don't think it really matters when you're choosing from this bunch. None of them are "sipping" rums, so all are apt to be mixed with something else. For my money, I'd go with the Bacardi, but only because I have more use for it than the Myers dark or the Captain Morgan spiced.

Thanks, do you generally prefer to go for the clear rum?

Take your spiced rum and use it in a simple highball like a rum and fruit juice of your choice or make yourself a rum punch.

I do, but only because I find it more versatile.

I like the El Dorado 12 y.o. from Guyana. ^

Having recieved my order I had a fun time testing those different bottles:

Diplomatico Reserva Exclusiva (Euro 33,49 incl. 19% VAT)
Very dark, a very balanced mild taste, hard to believe it has 40% alcohol in it as the taste of it is almost non-existant

Flor de Cana Centenario 12 Years (Euro 21,70 incl. 19%VAT)
Quite dark, not so fruitful and tasty as expected but still good, definitly taste the alcohol
and

Pyrat XO (euro 35,49 incl. 19%VAT)
The aroma is very orangy, the alcohol is quite present. Not as balanced as expected. Still very tasty.

Overall I would say that the 1st one is the Diplomatico by means of a balanced taste. But also it is 3rd in regards to recognizing it as a rum, for this to be the case it is too mild. (That bottle was emptied very fast with great joy!)
2nd is the Pyrat XO as its taste is too much in a single (oranges) direction. With the alcohol being quite present there was more respect to it and it will last longer...
3rd is The Flor de Cana, a quite decent rum with a nice taste to it. Also works well for aromatic cocktails.

Now I am curious how to get the really good stuff which those islands keep for themselves.

I've been a Myers's fan for, like, forever, and one time in an airline lounge I discovered Appleton Estate, which isn't half bad either. You can probably get it in a halfway decent DFS.

Honorable mention: Bacardi Limon, 70 proof, tastes like lemonade.

I quite enjoy Havana Club rum as a mixer (typically rum and coke for me), can be found in most duty free shops in Europe and should be in the same price range.

a new one made for drinking neat/straight - caliche

could also search luxury hotels forum for posts by stimpy (with "rum" in it) he said he tried an interesting one in london

Some airport duty free carries Stroh rum from Austria which is noteworthy as it is 80% alcohol. Made from sugar beets and intended to be mixed with tea (a teaspoon per cup of tea -- hence the high alcohol content). Very different from "drinking" rums and a bargain price.

Then there´s always "the adult rum":

http://www.rondejeremy.com/

It's actually not bad stuff. He knows the producers quite well.

I had the pleasure of sampling some with the man himself once. Obviously in public in a well lit room!

That's true - it's also a bit on the sickly side for me, but overall a pretty fantastic rum :)

If you want something with a bit more bite you could try Mount Gilboa - made by the guy who owns the distillery which Mount Gay uses for their premium rums. He likes whiskey himself, so has made a rum with a bit more of a alcoholic taste to it but which is nonetheless really well balanced.

The other brand to consider would be Plantation rum - a real rum by a rum lover.