what do you think is better coil springs or control arm? then tell us why.
You are talking about two completely different things! The control arms locate the position of the wheel and provides the pivots for the wheel to travel thru it's arc as you go over bumps lean into corners and such. The coil spring is what resists that motion and holds the vehicle up. You can't have a suspension without both.
Now if you really mean coils springs and torsion bars then you can make a comparison. In reality they are one in the same thing, the forces in the metal in a coil spring are identical to those in a torsion bar. One is not better than the other from that perspective.
Each has some distinct advantages over the other in certain situations.
Coil springs on a 2wd vehicle provide for a compact suspension design. A coil spring can be wound so it provides a progressive rate, that is softer in the intial travel of the suspension then getting stiffer as it gets closer to the limits.
On a 4wd vehicle with independant front suspension coil springs become less desirable because you have axles in between the upper and lower control arms. The coil would have to act on the upper control arm, this starts to make the suspension less compact and can start to dictate the styling of the front of the vehicle and intrude into the engine compartment. The torsion bar allows for the suspension to remain compact still acting on the lower control arm but being placed under the vehicle where it does not impact other design features. The torsion bar, however, can not pratically be made progressive (you would need a away to effectively shorten it as the suspension goes threw it's travel.
Hope this is the info you were looking for.