I have a 7 machine collection, and 3 of the 4 machines you mentioned are in it (no sttng - but my pinball brother-in-arms has one, and we try not to duplicate). Love them all. RS has been here the longest, never get bored, been a longtime Simpsons fan and my TSPP is beautiful, so it stays. WH20 is the newest addition, and I have no plans to turf it either. All are fantastic in the lineup, I don't think you could go wrong with any of them.
Would love a STTNG too, but read above...