There's no one right answer. If your review any discussion of keyboards you'll find plenty of passionate opinions, mostly related to the feel of each keyboard.
I have a first-generation 12.9" iPad Pro, so the Magic Keyboard is not an option for me. I've used the Smart Keyboard (not Folio) all this time. I've tried the Magic, though, and love the feel compared to the Smart. The feel of the Smart keyboard is still good enough for my needs - I don't do a whole lot of writing on my iPad these days. If I was using the iPad heavily for typing I might prefer to have a Magic Keyboard (for my next iPad, of course).
Still, when I was writing extensively on the iPad I was also traveling (iPad in backpack, wearing backpack all day long). The lighter weight of the Smart could become a consideration, but the difference isn't so great that I might not choose the heavier keyboard anyway.
One consideration might be airline tray tables - I'd imagine the higher position of the iPad when using the Magic Keyboard might affect just how well the iPad fits on the tray table.