*2004 reboot will be tagged (BSGn), if we go classic it will be tagged (BSGc)
Hundreds of Vipers/Raptors
12 Colony planets
Numerous space stations
Trillions of civilians
Millions of Cylon Raiders/Heavy Raiders
Millions of Cylon GenIII troops
Hundreds of GenIV infiltrators
This made for tv moive/pilot is referred to as either "the Fall" or "Ambush" and tells the asswhooping of "The Fall of the 12 Colonies". It's not even technically considered a battle as the 12 Colonies of Kobol suffer such utter surprise and defeat that only 2 of the 120 Battlestars mount any kind of resistance.
The ruthless precision of the attack resulted in swift decimation, nay utter elimination of colonial forces. Massive civilian and military casualties. The cylons had well prepared for the battle and infiltrated human form cylons over at least a 2 year period to plant cyber-attack vectors that allowed them to disable both fighters and battlestars. The only reason the Galactica survived to retreat was her analog and unnetworked simplicity. She would be the equivalent of the USS Enterprise ('61) carrier serving today, but it never was upgraded. She was a destined to be a museum piece and had probably a larger compliment aboard than she deserved for being demilled. Commander Adama being the old warhorse that he was refused to tuck tail and run, but knowing he was horribly unarmed laid course for a remote supply station. This was an absolute necessity if they had any hope of mounting a counter attack. They were forced to re-commission a number of older Viper fighters from museum pieces. Not ideal, but you make what you have work.
We see a lot of other interesting, but not battle critical recovery work. The XO has to make a terrible calculus call killing 87 deckhands by isolating a section of the ship and venting it to space, in order to extinguish a fire during Damage Control response. We see a small Raptor crew recover a number of civilians by lots out of a hat and flee Caprica. The civilian leadership is so crippled that the 43rd person in charge, the Secretary of Education, ends up the President. And we also see the debate between civilian and military leadership precedence during a conflict of pure survival.
In the end, this battle cleanly and clearly goes to the aggressors, the Cylons. They achieved a landslide victory through subterfuge, infiltration, cyber warfare and ruthless total war. The colonies had become soft and complacent and had no chance of preventing their own defeat once the trap was sprung. You can blame Baltar all you want for a single flaw in the planetary defenses and quite possibly for a cyber-attack vector against the vessels of the colonial fleet, but all that did was prevent effective resistance. The Cylons had surprise, guile, and cunning. The colonial fleet was caught flat footed and would very likely have fallen regardless, it just wouldn't have been so sound a pounding.