I've actually been going through this same bit of thought over the past few months. I've found that popularity seems to be split right down the middle between Cruisin and Rush. I have a slight preference to Rush, but enjoy both and would probably be happy with whichever is available for less. It's very common to hear that Rushes are available for $600, but in my area, I haven't found a single Rush for sale at all, let alone at that price point. I can locate Cruisin USAs anytime from $700 to 750.
As a wildcard in all of this, I can also have a Virtua Racing Twin *delivered* for less than what a single Cruisin or Rush unit will cost. I'm a fan of VR as well, which makes it a good option; however, it lacks the variety that I believe Cruisin USA and Rush both have. Team that with the upgradability of both Cruisin and Rush, and Virtua Racing becomes a tough sell, despite the low cost.