Perception

“A high Perception grants a bonus to the Explosives, Lockpick and Energy Weapons skills, and determines when red compass markings appear (which indicate threats).”

Perception’s big draw is that it increases the distance as which you notice threats-red marks on your compass. This is useful for letting you know where your enemies are before you engage, which allows you to avoid encounters, or get the drops on your foes. If tactical advantages don’t mean anything to you, obviously Perception shouldn’t be high on your list. Even without the threat markers Perception gives a bonus to three skills… which makes it fairly useful by that simple virtue alone. Many good perks require a Perception score of six, so that’s where you should start.