I have played 3 of the 5 1 watters, the JTM, JMP, and JCM. I own the JMP, and believe me when I say the thing kicks @ss. I also own a JMP 2203, the real deal, and they really sound alot alike. Granted, it is only 1 watt and it is going through a 10 speaker, but when you run through an external cab or especially slave through the FX loop of a bigger amp, it sings.
I liked the JTM, sounded great for the clean kinda stuff and low gain, Hendrix-y stuff. The JMP covers anything from hairy cleans to late 70's rock, especially with the extra pre-tube boost engaged. I did not like the JCM at all. It had the potential to be great but just did not deliver in my opinion. I was not thrilled with any tones I was getting. I highly recommend the JMP, it covers the most ground outside of the dual channel JVM, and with a good overdrive pedal your options are limitless. People complain about the price and only being 1 watt, etc. but these are great amps.