If you're talking about grounded armies of equal number facing off against each other, I think I'd have to give the edge to Fantasy.
But after the Sci-fi team loses that battle they can retreat to their starships and nuke the battlefield from orbit.
You have to keep in mind that Sci-fi includes a lot of space-travel, where any Fantasy story stays on one world, or maybe have parallel dimensions (which Sci-fi also has) at best. On the grand scale, Sci-Fi can't lose. Fantasy settings don't have the means to travel into space and launch a grand attack on the Death Star, Enterprise, Citadel, or any other space station you care to name, while the Sci-fi side has more than the means to invade any fantasy planet it wants, and just destroy it if they can't conquer it.
But after the Sci-fi team loses that battle they can retreat to their starships and nuke the battlefield from orbit.
You have to keep in mind that Sci-fi includes a lot of space-travel, where any Fantasy story stays on one world, or maybe have parallel dimensions (which Sci-fi also has) at best. On the grand scale, Sci-Fi can't lose. Fantasy settings don't have the means to travel into space and launch a grand attack on the Death Star, Enterprise, Citadel, or any other space station you care to name, while the Sci-fi side has more than the means to invade any fantasy planet it wants, and just destroy it if they can't conquer it.