This paper describes a comparison of material and device results obtained from AlGaN/GaN epitaxial HFET wafers from three commercial sources. Although all three sources supplied material to the same nominal specification, X-ray diffraction, Hall effect and C-V profiling revealed significant differences between them. Wafers from two of the suppliers showed poor inter-device isolation characteristics, indicative of a conducting buffer layer. Wafers from the third supplier showed excellent inter-device isolation, but C-V measurements showed that the AlGaN was about twice as thick as specified, resulting in devices with high pinch-off voltages ( similar to -16 V). For the wafers with poor buffer isolation, RF measurements on 1.2 mum gate length devices gave values of f(T) similar to 5.0 GHz and values of f(max) from 8.0 to 11.7 GHz (exact values depending on DC bias conditions), while for the wafer with over-thick AlGaN the corresponding values were 8.0 and 20.0 GHz.