It'd be nice to try them all out to see the differences. With my first rifle, I hope to purchase a decent fit, and then re-evaluate once I've gotten some time under my belt.
It sounds like with the Basic Rifle class, they'd cover a few differences/options/features to consider, but I'm not sure I'd get to try a few. That's one of the selling points of the open house, though - they will have represetatives from the gun manufacturers, and certified instructors.
I'm a fast learner, so I think I'd get a lot out of the open house and even more out of the First STEPS. It's just taking the leap of purchasing when I have no experience, so we'll see after this weekend.
Then there's also the issues of "breaking-in" a new rifle, but I'm not sure that can be avoided no matter which route I take.