Hard question.
I owned a RS for a few months. Cool game, but I had a proposal for an exchange I could not decline. I somewhat miss the game as it has plenty to offer in terms of PF layout (and being left handed, having 3 flippers on the left vs 1 on the right is fun and unusual!). But it seems the rules do not give this layout its full potential. It had everything to be as "rich" as TZ... but it is not.
I never owned WCS. Could not care less about soccer. Still, the game is fun and good. It may appeal to children (the goal is a cool feature) and does have lastability for decent players.
Bottom line is you can't get wrong with either choice. They are very, very different in terms of gameplay. Try them both, and find the one that fit your style!