I have remained so far out of the loop, my BoTF battles are hardly mentionable compared to the great tales on this thread. However, there are several memorable engagments:
1. I was the Federation, and had been harrassed by Klingon Destroyer II's for a ridiculously long time. They would just pick off any ships I sent to catch them, and would raid any time I wasn't there. So I finally scrounged up slightly smaller fleet of Constellation II's, and went at them with phasers blazing. They were fairly experienced, but overconfident (after that pasting we gave them on Archer IV ), and didn't know what they were up against. I could not belive the punishment that my destroyers took, but even after losing eight ships, the Klingons refused to retreat. Eventually I got them pinned between groups of two or three Constellations and hit them from all sides, which finished them off. I think I only lost three or four Constellations.
2. Also as the Federation, I finally goaded the Romulans to engage my fleet of heavy cruisers and Galaxies with their main battle fleet. There was a Romulan outpost, so I was able to operate in that first turn, which saved me. One of my ships destroyed their outpost while the rest evaded. Luckily, although quite a few fell, I ended up in a perfect tactical position surrounding a fleet of R'Derex II's. When the next turn came, my concentrated fire obliterated them.
3. As the Romulans, I was able to excecute a near perfect blitzkrieg against the Federation. They refused my offers of assistance for the last time, and my battle fleet was able to escape detection until it was too late. I declared war on them in the same turn that my attack began. The first turn was perfect, hitting every outpost in range catching the support elements and patrol ships. The Federation had relatively small territory but a large fleet. By the second turn, I had reached Sol. There the humans put up resistance, and I destroyed their entire battle fleet. Five turns later, the Federation fell.
4. As the Romulans, I was locked in mortal combat with a highly militant (and higly AI tech-cheating) Ferengi Alliance. They had been able to move through my space at will, destroying anything that stood in their way. It was disastrous for morale, but I was able to sacrifice one destroyer at a time to stop their transports. I finally had cruiser II's, and desperately needed a victory. A massive fleet of 40+ Ferengi vessels entered my territory. Amazingly, they didn't move away in that cheating manner that they do (I know full well they shouldn't have a CLUE where I am) . I scattered them with a swift strike of the cruisers and my remaining destroyers. I got all of their transports, and they fled my space. I followed. I then hit their primary outpost, bagging most of the Light Raider II's, and the next turn I caught the last of the War Cruisers. After about four turns, none of the Ferengi ships had survived, and I had enough experience that the key ships of my engagement lasted another 150 turns, only retiring with much fanfare when I upgraded my entire command fleet to heavy cruisers and Warbirds.

My favourites are always when a handful of Defiants make fireworks out of an entire Ferengi or Klingon fleet.
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Riker:"Tough litttle ship"
Worf:"LITTLE?!"

btw, Jakrok, you posted your reply as an entirely new thread, might want to delete it and post it here.

The best battle I ever had was when my 9 federation science vessels (all legendary experience) destroyed 3 ferengi Maruders. Never again I wasn't so proud of my fleet

There were of course many other huge (40 defiants and 30 dreadnoughts against 110 romulan fleet...) and interesting (7 sheliak riders vs 5 klingon heavy cruisers) battles, but can't say which was the greatest.