GOT is one of my least favorite pinball machines of all time. I find the rules design to be completely atrocious, incredibly unbalanced, and extremely unfun. The scoring is ridiculous and makes discrepancies that are both intimidating and defeating to new and casual players. On top of that I'd say the game has some of the worst artwork on any Stern machine, as well as dots that feel crampt and unable to properly convey the information they're trying to convey.
ACDC is one of the greatest pinball machines ever made. It has a fantastic balance of risk and reward, with each mode providing a fairly unique and relatively equally viable approach to playing the game. With both of these being Steve Ritchie designs they can tend to be a little grindy, so that's something to be aware of going into either option, however with ACDC having the Song Jackpot constantly looming over your head can make that grind feel more exciting.
I've played many, many games on both of these machines on location and in tournaments. One I hope to never play again, and one I would gladly own.