[Suicide Junkie]

In general for fleet combat, you will want to maximize your hitpoints * damage output.
Where hitpoints include all internals, armor and shields.

Be sure to take to-hit chances into account, as this will increase your effective hitpoints and reduce your effective damage.

This will maximize the amount of punishment you can dish out before being destroyed. (Or minimize the losses you take before winning)

Note that there will be a lot of rounding effects due to firing first, and crippled ships (for tiny fleets or single ships), and stuff like that.
Also, Special Tactics or Strategies, such as longer range weapons, or custom formations can also influence the results.