I have two best battles one in
EB and one in BI (well actually a series of them in BI that lasted for six hours in one turn)
My EB one was when i was playing as the Grey Death with M/H. I had one general deep into Egypt, i was just doing some RPing raiding with a big army, trying to slip past the front lines and get at Alexandria to stop them producing troops. I got half-way across the Nile Delta before they river blocked me. so i turned my army around for home,figuring that i could try again later. However then a seven star general with a full stack that had among it three units of those Galatians swordsmen and some of those elite phalagitias that they produce ( i forget the name ) cut off my retreat. We met up and i had my spear wallalong the red line to prevent total destruction of my army. I had many Pandotopoi phalanxes and a few of the heavier ones too. The battle strated out i had my general and some merc cavalry that i had hired for the fight (I saw it coming and was like oh crap) charging out on the left flank trying to get around their lines. Somehow the enemy general came out to meet these men ALONE. i was think this will be easy if i can kill him. However he simply WOULD NOT #@$$@$ING DIE!!!!!!!!. Then some of his spear infantry caught up with me, and tore my cavalry to sheards and killed my general as he was fleeing back to my lines. At this point i though it was over. Then the lines met. By some miracle it held. However the enemy generalcame swinging around MY flank to finish me off . However as he was attepmting to rout some spearmen, a unit of peltasts stopped right next to the fight behind him. I ordered them to throw at the general. First shot he fell dead. At this point the battle began to swing wildly. both armies broke twice at some point during the battle, however as soon as they got away from the fight they always rallied. I began to use my archers to kill off as many of the enemy as possible. However as soon as any missle unit got close they routed again and again and AGAIN!!!!!!
At this point i lost it at my computer and started yelling things that would make the sky fall on my head. However the tide finally turned as the enemy broke en-masse. Oh sure the rallied however they were unable to get back together for i used what remained of my cavalry to great effect, and kept them routing off the field. It took me an hour to fight that battle.

As for the BI one well The year was 402AD or 403AD (somewhere around there) and i was playing as the Huns. This was three years ago so forgive me if my memroy is rusty. I had spent most of the time obliterating Europe for lulz. Then i hit the WRE hard and took over most of it except Spain,(Where many of those Hordes went after i crushed them), britain and North Africa. Anyways i had a single general with a third of a stack of HAs and a heavy cav unit, on rebel patrol along the Rhine. Then i spot the ENTIRE FREAKING HORDE of Roxolani heading for a ford in the Rhine. I immedatley gathered up my general, stipped the region of mercs for the next 20 years and the local garrisons of several towns, (which in the end amounted to a half stack of HAs, Heavy cav and three infantry units), and i hurried to the ford at which i though the horde would cross at. Needless to say i didnt make it. and during one turn the horde attacked me one army at a time (TY GOD for stupid AIs). These were fresh hordes btw not the half stacks of depleteds, that run around after battles. I forgot how i did it but in five battles that took me from 2pm to 8pm i took those Roxolani from a full horde faction to broken remanats of troops that had managed to get away from the Hell-fields. At the start i had 1023 troop (I think) and at the end i had 127. I took on the last horde with 198 troops. At the end i got up and went to eat dinner and got myself a couple of Smirnoffs.