To me a "magic seat" is when the best seat on the ride isn't the front or back row but somewhere in the middle, just because it's so rare and almost seems to intuitively defy the laws of physics, with most of the optimal places on rides coming from the maximum amount of speed in/out of an element as it lags into it slower or is pulled out of it faster. Magic seats I know of include...
The Beast- Second to back, you get all the speed that comes with a back seat ride but without it being a wheel seat.
Magnum XL-200- Row 3 of the first car on the black train is known as the vomit seat or the ejector seat because the ejector there feels like it could almost kill a man, much more than you'd get in the front or back rows.
Ravine Flyer II- Front row of the second car, in a ride that involves both a lot of charging into elements and dropping off of them this is kind of a "sweet spot."
Wild Thing- Row 3, this isn't an "official" one but my friend Connor and I kind of found it back in July, you actually get some decent freaky darkened floater in the tunnel coming back to the station and it's a bit disorienting. Not nearly as nuts as the others I've listed though.
Blue Streak- Second row of the first car, it's glass smooth not being on a wheel but you're still in the front and it's still a mess of airtime.
Wild One- See Above
Phoenix- Row 3, the back row of the front car is notorious for taking possibly the best buzz bar airtime to the next level
Think there are a few more but these are the ones I can think of off the top of my head.