The most used PCB design softwares: Allegro, PADS, Altium Designer (high version of Protel).
Altium Designer is more suitable for simple and mid-end boards, and which is easy to get started;
While Allegro and PADS is mainly used for designing high-end and complex boards. BTW, Allegro is pretty flexible than PADS so that it is more advantageous to make high-density and huge boards.
Besides, other PCB Design softwares like Orcad, PCAD and Egle are less used.
