Like others have said, depends on what the magic is capable of, but I would give the advantage to the modern military. Could a dragon or griffon stand up to modern fighter jets who are able to fly faster and higher? Could a magical ground force withstand modern artillery and/or bombers? Could they produce shields or other countermeasures to protect themselves from those kinds of munitions? How would archers and mages fare against modern rifles that could engage them from hundreds of yards/meters away? Also, the greatest weapon in any war is information. The modern military (assuming the battlefield is somewhere on Earth) would have access to real-time info from satellites, radar, etc. Would the magical military have anything similar?
I drive a 2018 Subaru Forester. I got it because I wanted a SUV with AWD and a turbo charger. My previous vehicle was a Camaro, and while I loved driving it, having a RWD car in the winter sucks, and I had recently bought a house, so having a vehicle that can carry more than just groceries made sense.
I was driving the Camaro around Xmas time and there was a light dusting of snow on the highway. I hit a patch of it and started to fish tail, and that scared the hell out of me, so I traded it for the Forester the following fall. The Forester has handled any conditions I’ve come across so far like a champ, including heavy rain, snow, ice, and muddy hillsides.
Trading the Camaro in and getting the Forester marked the transition (in my mind) from being a young adult, to becoming an older, more sensible one. I was driving home from work one day, and a Camaro passed me on the highway. I couldn’t help but sigh and ask myself why I had to get old. The Forester is a good vehicle and very nice (got the XT Touring package), but the Camaro was way more fun to drive, and I still miss it. I’d like to get another sports car in the future, but we’ll see if that happens.