With a green field installation 10gbps network (no legacy equipment to support), why would one select one physical medium over the other? If left to impulse, I'd probably go with fiber optics over twisted pair because it is new and exciting. (Sparkly Pony!) But really, this should be a rational, logical decision.
I've very much interested in the "why" behind answers. E.g.: "Fiber performance can be degraded when placed near Kryptonite", "TP is 1000 times cheaper" etc.
(Background: I ask because I have a need to upgrade our Internet web/streaming servers network infrastructure at the data center.)