It seems to me in auto combat the game simply takes the ratings of the two armies and calculates result from that. This can mean significantly different outcomes depending on whether you fight manually or automatically.

I'd suggest using auto combat whenever your army rating is higher than enemy rating, as it usually results in much less damage taken by you. Also, auto combat sometimes lets you win fights that would be impossible to win manually, especially when the enemy has special abilities like coal stones etc.

On the other hand, fights where the enemy army is rated equal or stronger than your army should be fought manually as they can sometimes be won where auto would result in a loss every time.

(an interesting side note - assuming you win, in most auto fights all damage by the other side is done to the last unit in your stack. It may be worthwhile to make sure the last unit is a tank-type, and at full health, before initiating auto combat)

These hidden polls (I never really check the poll area, except when people post a forum thread about the polls )

Quick-combat right now is fairly rubbish, I almost always can get a severely better outcome by fighting on the tactical map, most of the time because the units that die in auto-combat I personally would have protected... (well duh).
I think one thing Quick combat forgets is that there is a certain range between armies at the start of the map, giving archers theyre advantage, and letting melee's on the archer heavy side set up a defensive line.

Sincerely
~ Kongdej

autoresolve is terrible if you use archers, beasts, or any other kind of low-defense unit, or any units which aren't at full health.

it seems to automatically allow the enemy team to do a certain amount of damage, and it distributes that damage in an overflowing single-target manner, starting with the lowest HP unit

it's really pretty broken. my familiar can't be killed if the enemy doesn't have archers, i'd protect him too well!