Babylon 5 vs. Battlestar Galactica
These two settings tend to get bodied against a lot of other sci-fi when we take just the humans. Therefore, why not put the humans against each other?
On one side we have Babylon 5 itself - a very large space station that originally served to maintain diplomacy across the stars until Earth descended into a brutal dictatorship and all the aliens decided to kill each other. Joining them are The Alexander and Churchill battleships along with all the "enemy" ships from the battle for B5 Independence; the Roanoke, Nimrod, Olympic, and 3 Hyperion class heavy cruisers, 2 earthforce gunships, a bunch of boarding pods and a compliment of marine forces. They'll also have a lot of starfuries.
Even with all that they'll be heavily outnumbered however, as they'll be fighting the Battlestar Galactica and the entire fleet of humanity at full strength. Even if it's ragtag, they probably have 50 ships to B5's 10. That said, B5 is huge and well armed.
The Fleet are the aggressors. They're going to try to conquer B5 and use it to defeat the Cylons or something. B5 will try to drive them off. This doesn't need to be a battle of annihilation. Both sides are led by their most competent commanders.
EDIT:
Round two: It's just the Alexander and Churchill fighting alongside B5. BSG still gets it all.
Bonus Round: The Cylons vs. Minbari.