Unlike in-sector combat, which is full of variables almost to the point of being unpredictable (especially if you mix in player skill), out-of-sector combat relies on a simple algorithm to determine the outcome. Given this, what ships or fleets will be the best at OOS combat, with the following considerations being used to determine "best", in order of importance:
Survivability. Replacing lost ships is a massive chore, and whoever is left alive at the end of the engagement is by definition the winner, so this is top priority.
Least amount of player interaction during service. With over 200 sectors, manually managing fleets can quickly become a full-time task.
Ability to engage targets at arbitrary locations.
FPS impact. Deploying 100 lasertowers around every jump gate and beacon may be effective, but will destroy in-sector FPS, making a whole part of the universe a no-fly zone for the player.
Least amount of player interaction during setup. This includes things like creating a massive complex and a fleet of AI ships to distribute missiles to M7Ms or M8s.