Undertale- Dummy! vs Castlevania: Symphony of the Night- Dracula’s Castle: Dummy! is a strong candidate for one of my favorite Undertale songs overall, which is not an easy thing to be.
Shadow of the Colossus- Demise of the Ritual vs No More Heroes 2- Philistine: Not exactly the hugest fan, but this is one of the completely non-interesting SotC songs to me, so it's good enough.
Zero Escape: Zero Time Dilemma- Blue Bird Lamentation (2nd) vs Bastion- Settling Sail, Coming Home: If the Bastion song was either Build That Wall or Mother, I'm Here on their own, this would've been a stomp even though I REALLY like the ZE song, but I'm just not a big fan of the layered vocals here. Actually, MOST of Bastion's soundtrack would've probably won here, but that's all personal bias. >_>
Metal Gear Solid 2- Main Theme vs SaGa Frontier- Last Battle T260G: Jams much harder. Much, much harder.
Final Fantasy XIV: Heavensward- Metal vs Fire Emblem Fates- Thorn In You: Didn't we just have this three pools ago? Oh wait no, that was ANOTHER song from the same battle with the same godawful voice synth. My bad. Generic FE music easily takes it.
Persona 3- The Battle for Everyone’s Souls vs Final Fantasy XIII- Fang’s Theme: This was actually VERY close, as Fang's Theme absolutely plays to my tastes, but Battle for Everyone's Souls is just... well, much cooler, and plays to my tastes in an entirely different direction.
World of Warcraft: Wrath of the Lich King- Bronze Jam vs Caligula- Distorted Happiness: Utter stomp.
Ducktales Remastered- Mount Vesuvius Theme vs Xenoblade Chronicles- Crisis: And here we have arguably one of my favorite songs in general, let alone in video games. Easy vote, own nom bias and all.