I've experienced both.
The last batch I bought, the two RTGG's were cranky and aggressive. Picking on each other and my oscars, so I sold them.
I bought a pink GG and a juvie RTGG, the RTGG got pwned by my gold saum, and the pink was trying to kill everything else, so I sold the pink.
Those were all housed with several gold saums, polypterus, sevs, and a pair of oscars.
I decided to try one more time because I found a really nice RTGG for a great price I couldn't pass up, and this one has been suuper easy going. No aggression to any other fish, and the gold saum doesn't seem to mind sharing it's turf with it.