I think you are referring to the tubes that carry the pushrods that operate the valves.
Valves cannot open and close very quickly so they limit the maximum revolutions on a 4 stroke. 2 strokes can rev more.

2 strokes are cheaper to buy and there is less to go wrong. Only buy a 4 stroke if noise is a problem , fuel economy is important or you do not like a large silencer hanging out of the model.
A plain bearing 2 stroke of a reliable make will give long service without much trouble.