Next time you find yourself in the midst of cocktailers and you are just about to grab the bartender’s attention and ask for a martini (or manhattan or Rob Roy – or anything fancy for that matter), decide first how you are going to want your drink. Otherwise, the bartender might have to ask you, “Would you like it shaken or stirred?”

If you are not sure which one’s better, read on!
Already know what you prefer? Great! But do you know why? If you want to know why, read on as well!

There have been some experiments carried out by cocktail enthusiasts, bartenders and even scientists (YES! REAL Scientists!) to dissect the difference in the end product prepared by those two methods.

Check out the conclusion by two scientists (actually a professor and a graduate student) from Harvard University here: At Boston bar, Harvard scientists find physics at work
Check out the conclusion by cocktail enthusiast Doug here: Shaken v.s. Stirred – has some delicious reference to other articles.
Check out the conclusion by yet another D.C. cocktail enthusiast here: Shaken v.s. Stirred

Short conclusion:
If you don’t have time, we don’t want to bore you with the nitty-gritty either.
Basically, if you like your drinks thicker-tasting, cloudier-looking / foamy, “getting more bang for the buck” – more volume, though that’s really just melted ice, a.k.a. water, floating along with your alcohol and colder, then go with shaken.
If you like your drinks lighter-tasting, clearer, alcoholic – the way it should taste – dry, harsh, crispy, then go with stirred.
If you don’t know and you don’t care about all these, as long as the drink looks nice and tastes nice – and that’s perfectly fine as well – just make sure you tip the bartender, because he/she deserve you a drink for which you can’t complain.

In the end, what makes a drink great is how much it appeals to the person holding the glass – a real tip by a real bartender.