I think you have a situation here where either solution is correct. Fiber will definitely give you better protection against lightning. However, with a short distance of 120 feet, its not going to make much difference, even with DB and protectors if you take a hit that close. I remember an old Qwest tech telling me anything under a 150 feet, and protectors aren't going to matter.
It depends on equipment too. Our customers that have multiple building type environments usually opt for fiber connectivety between switches. So it actually makes sense to run fiber, regardless of distance. If your connecting the other building to run an 8 port SOHO switch, then run a strand of gel filled Cat5 through the conduit and be done with it.
