I would say Gorgar but I am biased and most likely in the minority.
Both are great though. Black hole has that tough multiball but Gorgar is just awesome to look at and can be a toughie too.
You win either way!

Condition would be key too.

Are you trading you Magic Castle by chance? That looks like a cool game too.

Sounds like a good deal both ways. Seeing as you are getting a Flash Gordon too get the Black Hole. Would be too much red w/ gorgar. Also, Flash Gordon is a ball breaker like Gorgar. Unless you are a glutton for punishment