Quoted from FrankJ:
I've owned both. I prefer Palace Guard by a mile.
Hit either row of 4 snap targets for an extra ball. Hit A-E on top for an extra ball (no need to hit "C" last). The bottom outlanes and center drain are also A-E switches to help build extra balls.
Scoring is more balanced, as there are no 500 point shots. Hitting snap targets either light 10 point pop bumpers or 100 point upper targets. It makes the pop bumper area much more valuable.
It's a classic GTL add-a-ball where you can be on your last ball, terrible score, and have a great ball and build back up a few balls and end up with a great score. You are never out of the game. On Royal Guard, hit the wrong letter on top or miss a 500 point exit and you're pretty much screwed.
That's what makes Royal Guard a tough game.
It's very possible, either by a bounced flipper shot or the pop bumpers, to collect some of those upper letters with other than a plunger shot. It's a good idea sometimes to not just bang away at the snap targets, especially if you've got some of the upper targets lit for 100 points. Sometimes the ball will go up there, right through one of the lanes, and come down through another, and you've collected two of them without a plunger shot at all. Many times I've had all of them but the C lit for the third plunger shot. You can collect three specials if you're good with the plunger shot.
I think it's a great game. Very underrated. I completely restored mine and while it's tough to say never, it would be really, really hard for me to sell it. It was my first complete restoration, and it's a great player to go with it. It can be a drain monster at time, but if you can get the specials lit on the fan targets, you can rack up some games.