I've been using pull-pull on rudder and the fiberglass Dave Brown for elevators on my last two planes and like them. My next one I'll try some carbon fiber rods. I've used 2-56 and 4-40 rods in plastic sleeves, wood dowels with 2-56 rod strapped to it, and all worked well. I don't think it matters much as long as you use the appropriate strength system for your requirements. Of course the all-out competitors may require the utmost strength and low weight of CF/titanium, but for sport, I don't think it matters that much if installed correctly!.