Hardrock disc or not?

pros
when you break spokes on your wheel, which happens rather often, with disc brakes you can still use your bike without problems until you repair your wheel.
With V-brakes the rim of the damaged wheel will touch the brakes slowing you down.

cons
if you use disc brakes on the rear and you want to install a rack to carry panniers for example, then you will need a special rack for disc brakes which are not easy to find yet.

design9r said:

what's the difference between the disc brakes and the regular ones? (i know they are better but why? and for what situations?)

Disc brakes will generally stop you quicker and are not as affected by weather as rim brakes are -- so disc brakes make it easier to stop quickly in rain/snow/mud).

Rim brakes are a good bit cheaper and also weigh a decent bit less, if you are concerned with weight. Also, many people recommend rim brakes for folks who go on long bicycle tours because the general thought is that you will have an easier time getting them repaired wherever you are -- but this may be changing as disc brakes become more popular.