I'm building an ARF and can only put in either Aileron and Elevator or Rudder and Elevator controls. Which is more crucial, ailerons or rudder control...........or do I need both?

Depends on the plane. A little aerobatic like the wild thing uses no dihedral and ail/elevator. A trainer would use a lot of dihedral and rudder/elevator. What plane is it?

I would think you want Aileron/elevator, but I would question why your limited to the choices you gave, and what plane your building. The above answer I gave wouldnt work well in a trainer.

The kadet senior has only rudder and elevator.

It also has a lot of dihedral....6 inches...its a very stable plane to fly.

On the other hand, i fly most of my other trainer type planes with only aileron and elevator with less dihedral.

Rudder is very handy for steering on the ground though.....if possible, i would go with all three.....you don't have to use the rudder if you don't want.

ailerons are more useful in the long run, rudder trainers are often slow to respond and while some say that gives thinking time, it also dun help you save it at low speed on landing runs.
but for a few $ why dont you buy another servo and have all three?

The plane is an A-10.......the problem i have with the rudder is since its rudders are past the ends of the elevator on the tail I'm unsure how to set up a servo to concurrently move both of them?

1. you dont need rudders then
2. use a two arm servo and link one rudder to each side with thin snake or wire ( for small A-10 eg park flyer, RUDDER NOT NEEDED ON THIS THO )
3. if its a bit bigger plane use a bell crank in the tail to link both rudders together and to the servo.
4. forget rudders
5. you dont need rudders
6. you know by now

If I had to choose between the two I would definitely use ailerons on an A-10. I don't think it would fly very realistically with just rudders.