My suggestion depends on you and your riding location/style. If you really like to hammer and you are on fairly smooth roads, get the FX. Having used cantilever, caliper and v-brakes in all kinds of conditions, from dry to wet/icy, I can tell you they still work. They may not be as nice as discs, but you will stop which is what you need.

If you ride in an urban jungle with potholes galore or like to saunter rather than hammer, I'd go with the SU. 26" wheels contribute to lower gearing (along with the gearing itself) and they are stronger than 700c wheels to hold up to the pounding of the urban roads.

Finally, if you ever want to do sport riding, I'd get the FX. It isn't a road bike, but I think you would find it to be much nicer for an afternoon out than the SU. Happy shopping.