What is a quality FM adapter for my car that I can use for sirius/xm as well as mp3 (not an iPOD)?

I know they heave wireless FM xmtrs out there, but I haven't heard too many positive things about them. Am I better off hard-wiring an FM modulator directly into my antenna input or would it be more feasible in the long run to change out my stereo to one of the newer models that already comes with the RF input? I would like to hear from those that have already installed any of these into their vehicles.