I own the HGA 1.1, and can safely recommend it. Here's my quick review of the system:
Composite output: TERRIBLE. The colors bleed, are blurry, and thin diagonal lines run along the screen. Don't even think about getting an HGA unless you have an S-Video TV. My TV does have S-Video, so the composite output isn't important to me.
S-Video output: Very good. Unfortunately, I don't have a home cart system to compare picture quality between that and an HGA. I do have a Neo CD, however. What I can say is that the S-Video output on the HGA is very good, but not quite as good as an S-Video picture coming from a Neo CD. So using the Neo CD as a reference, the HGA's S-Video is better than the Neo CD's composite, and almost as good as the Neo CD's S-Video output. Overall, I'm pleased with the picture quality.
Joysticks: Unfortunately, they do have the Capcom setup of 3 buttons on top, 3 on the bottom. The top row of buttons are A B C, and the 3rd button on the bottom row is D. It's like this:
A B C
x x D
The joystick itself was pretty stiff when I first got it, but after a few months of play, it's loosened a bit. I didn't like it very much at first, but now that I've broken it in a little bit, I like it much more. They joystick and buttons feel pretty solid. I like it more than my bean-style Neo CD joystick. My only complaint about the joystick now is the placement of the D button. I hope GW Trading releases a stick with a more Neo-friendly 4 button setup. It's not a fatal flaw, but it's not optimal either.
HGA unit itself: Pretty nice. It runs quietly when you have the lid closed. It also has independent Red, Green, and Blue controls, which is both a plus and a minus. It's good in that you can REALLY fine tune the color output, but it's bad in that it can be a bit of a pain finding the perfect blend of red, green, and blue. I eventually found a combination that I liked, and now I'm pleased with the color.
There's also a dial that's sort of like a picture adjust. If you turn it a little bit, not much happens. If you turn it a lot, the picture will really start to scramble. Just crank it all the way to the right and forget about it. It's not that useful on my TV, but may be crucial for other TVs. I don't know.
Overall: I think the HGA is a good purchase. Nice picture quality on S-Video, and everything seems to be built pretty well. I'm not sure how it compares to a Super Nova though. The main reason why I bought an HGA is because when I was looking for a system like this, I emailed both MAS and GW. GW responded to my emails; MAS did not. MAS didn't want my money, and GW did.
And I'm happy with my purchase!