I'd rank them:
1. WCS94
2. Tommy
3. Demo
4. Space Station
Ranking to me doesn't mean much. Everyone has their own personal preference on pins in the forum. Is there a game out of there that you really don't play as much as you used to or do they get equal play? I'd cover up one of the machines and stop playing it for a certain amount of time (30 days, 45 days, etc). See if you miss it. If you don't, then it's likely that it's time to move on from that machine and add another one that you might enjoy in your home setting.