Following amit's post, ADS is not a good tool for PCB layout. It's much better suited to circuit analysis and complex simulations. It's a design tool, not a general layout application.
If you are doing complex microwave structures (microstrip transmission lines, couplers, hybrids, coupled-line filters, band-gap filters, microstrip antennas, stripline circuits, etc), then the ADS Layout tool is very powerful (especially when running Momentum, their "3D" EM solver).
I wouldn't mess with ADS for low frequency board layout (minimal pre-built part footprints, no nice trace-routing tools, etc). Stick with PADS, ExpressPCB, and other cheap/free toolsets for that. For developing and analyzing the electrical circuit, that's where ADS shines (think PSPICE on steroids ;-) ).