I've got both, 70-200 and the 135, and If I can, I'll always grab the 135. Stunning piece of gear.
however, if my only other lens was a 17-40 F4 lens, I think I'd be going for a 70-200 2.8 lens. there will be times you want something between the 40 and 135, and unless your planning to quickly add a 50mm or 85mm, then go for the zoom.