Question

Considering secondary effects, power and accuracy

Answer 1

By optimistic, I assume you mean the most balanced and versatile.

I'd have to say that Brick break is the most optimistic Fighting-type attack. It has reliable power (With a decent Attack stat, it packs just enough power to OHKO most variations of Aggron), along with a healthy PP capacity.

It also has the useful utility of breaking through Reflect and Light screen, which is very useful.

Lastly, Brick Break is a TM, and has incredibly wide spread (If a Pokemon has hands or some kind of blunt-headed limb or tail, it can probably learn Brick break).

Answer 2

Drain Punch, hands down.
Good power, perfect accuracy and HP drain all in a single punch.
The only downside is the PP, but it's not really meant to be used constantly, just for when the HP are low.