I went to a pinball show where a WCS94 was for sale and on freeplay. I wasn't really expecting to enjoy it at all, but I ended up loving it, and I bought it. The only thing that bummed me out was getting it home and trying to buy new ramps for it (as the ones it had were cracked), man were those just about impossible to find. So beware on cracked ramps. Someday Pinball Inc. says they'll make a set, but when, I don't know. There's no hurry on them. Also look out for excessive saucer wear. There are 3 saucers and they see a lot of use. You can patch those up and drop in Cliffy and Mantis saucer protectors.
WCS94 has great flowing ramps, a cool toy in the goalie, and a couple of magnets including one you can activate to try to save a center drain. The rules are straightforward and fun. The goal is to get to the World Cup final and beat Germany. The cool thing is you can do this 2 ways, by getting tickets and traveling to each city until you reach the finals, or by getting multiball and beating each team standing in your way until you reach Germany (and what a fun multiball WCS94 has, one of my favorites). The saucer in front of the goal is cool in that you can shoot the ball into the goal from there with a flipper button. The playfield is also laid out really well, and you get some cool ricochet action which can make for some cool goals.
I played RBION a few times and it didn't instantly hook me like WCS94 did. However, it seems really mysterious in both ruleset and theme, and it has me wanting to play it more to explore it, kind of like TZ. In fact, since Lawlor designed it, I wonder if he was trying to give Stern their own TZ type game with RBION. I'd like to have it in my collection someday to explore it more.
You probably can't go wrong with either, but WCS94 offers straightforward easily accessible fun (visitors love it), while RBION seems to offer more of a technical challenge, at least to me anyway. As such, RBION may find longer life in a collection by offering a greater and longer lasting challenge.