The path of higher resistance is safer anyways. Go with 330ohm. If they're too bright, step up the resistor to a 400 or a 500ohm resistor. If they're too dim, drop to 300 or 250ohms. Try not to drop too low, as if you give the LED too much current it'll go kaput.
Also, lifetime is a non-issue, as most LED's run for upwards of 20,000hrs at their designed specs. Now keep in mind there's 8,544 hours in a year and chances are you turn you computer off at least occassionally, so at normal specs that's 2+ years before replacing them.
Does the packaging or LED specs anywhere say it's mcd rating? That'll give you a good idea of it's brightness.