I quite liked the battle on the Moon in #41 of the Marvel series

Megatron vs the Predacons in #25 was cool too.

Galvatron vs the Cybertron Seven in UK #101 was pretty brutal.

Tracks, Bumblebee and Blue Streak vs Menasor from the original animated series also sticks in my mind ("Do you think that will really hold him?" "Off hand I'd say.... not at all".)