If considering the SuperTourist, the DX is a more versatile design. You may not be contemplating doing anything but commuting at this point, but you may decide to do some light touring some day. Or you might get to the point where you're commuting and then decide (get tasked) to stop by the store on the way home. Those occasions, your normal load can go in a trunk bag and you can bring along a couple of utility/grocery panniers- leave those folded up until you need them.

As far as the spring- some people like them, others question the sanity of the ones who do. Can be handy to secure a jacket or a ball, could help secure saddlebag panniers, think I've seen a couple of products (baskets mostly) on Amazon that are designed to slide onto the spring arm- even saw a youtube vid of a guy who made some DIY panniers using boating dry boxes that placed the hooks under the spring arm and then used a Kryptonite to lock the spring arm to the rack.