You can't beat a name sniper. They're designed to update their account's name within milliseconds of the new name becoming available; there have been cases of multiple snipers getting a single name at the exact same time such that both accounts end up with the same name. Mojang usually intervenes in those situations but it just goes to show how quick snipers are.
If the name you're after is extremely desirable and you're sure there are people sniping it then you're already out of luck. If you have any doubt about it being sniped, however, then there's no harm in trying to get the name manually.