Let's say that all creatures from the planets were working in unison to fight the other planet. If this is the case I believe that Roshar would win by far. Scadrial has Kandra and Koloss which are a large advantage but Roshar has 1. Soulcasters which are insanely useful in a battle 2. Parshendi/Voidbringers which can use the multiple different forms and 3. Chasmfiends. Try attacking a huge armored beast with regular swords. Not going to work very well. That's just my opinion though.