For me its,

Megatron with Devastator VS Starscream with Bruticus... shame Menasor had to sneak in. It would've been awesome if it was an all out equal battle royale instead then we'll see who's really the baddest of em gestalts.

The fight between Sky Lynx vs Predaking

Devastator vs Dinobots

Blaster vs Soundwave . Not the all out death battle but the sonic blast exchange in that episode about the hypnotic disco thingie

War of the dinobots

Aerialbots vs Stunticons - the first episodes when thy were both created.