A +2 for High Ground at best, and no penalty for low ground since the enemy on high ground can sometimes choose to move out of line of sight where you can't even target them. A +2/-2 swing would still be so powerful it would be the focus in every fight.
I like +1/-2 because it leads to counterplay and an interesting balance between saves and attack rolls. Save spells can't get that easy +1 to hit but they don't have to worry about getting hit by -2 penalties. +2/-0 is clean but it's still a straight buff to ranged weapons while offering nothing to save based spells.