I think the wave-port is more accurate (closer to measurement) than the lumped-gap source for any problem. The problem is it is difficult to define the wave port in some cases.
I usually only used lumped port when analysing an internal impedance in the structure. Waveguide ports are the one to use on CPW, but you have to take care to define the dimension of the port correct. Make sure that you only propagate CPW mode form the port and not other strange waveguide modes. Do a port simulation and look at the field in the port!!!