Optera 
The Alicorns seem hesitant to go all out. Fighting with that mindset the princesses have lost again and again.
However if neither side held back, it would probably go to the Alicorns.
Among the unicorns only Starlight and Tempest have shown to be capable fighters, the others are glass cannons or support while the alicorns can take a fair beating, see the flashback of Luna vs Celestia.
However if neither side held back, it would probably go to the Alicorns.
Among the unicorns only Starlight and Tempest have shown to be capable fighters, the others are glass cannons or support while the alicorns can take a fair beating, see the flashback of Luna vs Celestia.