The most important score is subjective, as it would vary from class to class.
Least important score? It depends on what party you were trying to build. Probably charisma or intelligence, as you rarely need more than one 'face man' or 'skill b****'. Maybe even strength.
I'm a bit on the opposite end, myself, but I can see it working out that way with an 'optimized' party. Constitution is important to everyone for hit points, Dexterity for AC and ranged to hit (and even melee to hit with Weapon Finesse), and Wisdom for will saves, spot checks, listen checks, etc. Strength would be on the high end for tanks and such, but depending on how many of those their were, might be towards the bottom.
Overall, I'd say it went like this:
Strength / Wisdom