Ext port one had slightly better video, but mostly known for having a much better sound chip that had richer sound and made certain instruments stick out more. However I think some with ext ports are based on later boards that have weaker sound and video. Easiest way you tell you have better quality genesis model 1 is if it doesn't have tmss screen.
well, one has an extension port, and the other does not. that would be one main difference. i have heard and read that the early versions with the ext port have better sound and/or video quality but nothing concrete and i've not had one to check for differences.
I have the non-High Definition Graphics one with no EXT port (the one with an empty plastic space to the left of the connectors) and the RGB video quality is really good. Very clear and nice colors. Very good stereo audio from the headphone port as well. I also have a model 2 Genesis, and the model 1 is far superior both in video and sound. It does suffer very slightly from jailbars, but the effect is so subtle you don't notice it most of the time. Supposedly it uses the original sound chip, so that's probably why it sounds so good. I haven't tried the composite out for quite some time, so I can't comment on that.
I had a SMD (actually, I think I still have it...) that was a pain in the arse when it came to the 50/60hz and language switches. Would change the switches to put it into its different modes, but region-protected games wouldn't get over the fact it was a PAL SMD. Had no idea why it was so cranky either. Pretty sure it has the ext port, but I don't know what revision it was.
