Guys,
I'm just starting to get into larger aircraft, and could use a little terminology help.
As I understand it, a pull-pull system for a rudder is where some type of wire cable or similar material is used to pull the rudder in each direction.
A push-pull system is where two stiff rods are used to pull the rudder, while at the SAME time push the rudder.
If this is correct, which system is more commonly used?

I'm also in the dilema of using dual elevator servos, as I hear they are hard to get tuned to operate in sync.
Thanks for any help fellas.

you are correct with the push/pull terminology. Pull-pull is most common. Any string that does not stretch much can be used. Fishing leader line, kevlar thread, etc. The hobby shops sell kits that include the string and some rigging for the ends.

The best setup for two elevator servos is that both elevator halves operate independently -- that is, they are not physically connected. Use a reversing "Y" cable from your receiver to the servos. If both servos are more or less the same, both elevator halves will go up and down about the same amount. If you have a fancy radio you can plug one elevator into a separate channel (e.g. AUX2) and mix 100% of elevator into AUX2. If one half goes up when the other half goes down, then change the mix to minus-100%. On most planes it really doesn't matter if one half goes up or down a little more than the other half. Also, depending upon the transmitter, the elevator trim tab on the transmitter face may only affect one of the elevator halves. Again, for most sport planes, this is not a problem.

The decision to go with a pull-pull setup usually rests on how the plane will balance out. If it needs tail weight, the servos are installed on the rear (push-pull). If the plane is already tail heavy, then a pull-pull is used which locates the servo/servos much further forward.