Stealth vs what?

[Kromm]

Skills like Camouflage and Stealth normally go up against straight Per (or Vision or Hearing, where applicable). If your Observation happens to be at Per+1 or better, you may use it instead. That isn't the main use of Observation, though, but a nice side-benefit having the skill. Observation's principal use is covertly gathering intelligence in the manner of a spy, a detective on stakeout, a military scout, or a gangster casing a mark: defenses, security, staffing levels, alertness levels, shift changes, objectives of strategic interest, etc.

As for when it's a Quick Contest, the easiest way to think of it is like this:

• When Stealth could actually achieve total surprise, roll a straight success roll. Success grants total surprise.
• When Stealth could at most grant the sneaky party partial surprise, roll a Quick Contest. Victory grants partial surprise.

This decision is necessarily subjective . . . the GM may or may not accept "I'm on alert!" as good enough to shift the first case to the second, and might even wish to tie the choice of mechanics used to a plot point, not rules action.