The problem with the question is that Sir Thorncrest isn't really asking where we would put our highest stat - he's asking where we would put all those 13's. Let's take a look:
Strength: If this is 18, then you're pretty much a fighter or barbarian. Hit points won't be great, but a +1 per HD (13 Con) is some help. Dex will be enough to qualify for some feats, but you probably wouldn't be an archer. A barbarian won't have a good AC, won't have a lot of hit points, won't have a good Will save, but he'll be able to dish out a lot of damage when raging. Is that enough?
Dexterity: If this is 18, then fighter, ranger, rogue are possibilities. Even barbarian, if you plan to use rage or buffs to compensate for the 13 Strength. Again, hit points won't be great so you may lack staying power. An archer-type seems best suited for this. Rogue could work, as long as you avoid melee.
Constitution: If this is 18, what class makes sense? No full spellcasting classes - a 13 in your primary spellcasting stat is not good. Paladin might work, as a high wisdom isn't usually critical to the class's spells.
Intelligence: If this is 18, you'll have good skill points. You'd also be a good wizard (13 in all others stats is actually pretty good, though I'd rather have a higher Con and a lower Str score). No other class makes sense with this selection.
Wisdom: If this is 18, then we're looking at druid, cleric, monk. Druid's have wildshape, so they're less affected by having 13's in the physical stats. Clerics, however, can wear heavy armor and have some good buff/healing spells, so that works. The monk would be above average, but not much. A high wisdom helps, but a great monk really needs good Str and Dex. The curse of MAD.
Charisma: If this is 18, then we're looking at a bard or sorcerer. Sorcerer works well, though skill points will be low. Bard is a problem no matter what their stats (IMO), but if someone must play a bard, this could work adequately. It would be interesting to play a paladin with an 18 charisma. He wouldn't excel in combat (at least not without some good buffs), but his saves and special abilities would be outstanding.
Note, all the above assumes core classes and no racial adjustments. Once you start adding all the other variables, it gets messy.
BTW, I voted Wisdom, as I think a druid with these stats would be quite playable.