This ask is like asking me to choose between my hands or something – I’m attached to both! Seriously sweet merlin I love both.
I mean fantasy is magic and monsters and nothing we were ever trained for. Sci-fi is aliens and spaceships and any kind of cool tech toys you want to write about. Mashing them together is fun. That way you can have both. Although I suppose in doing so I reveal my answer.
At the end of the day I come down on the “magic is science we don’t yet understand” side. I look at fantasy through a sci-fi lens. I love Stargate a little more than I love Once Upon a Time. So there it is really. Give me my space battles, and alien invasions. Give me energy shields, and energy weapons and Iron Man suits and transport beams.
Though I still think mashing them together is best. I just don’t like to choose.