Hello, I just want to respond for anyone else like me out there who was wondering this very same thing and googled it - and was directed here pretty much.
I prefer the 20B's over the 30's. As far as picture quality, I'm the opposite, I believe the 20B's looked better for picture quality, but that could be in my head as well. But one thing for sure is the cosmetics and comfort of the 20B's. The 30's are more narrow, and the lens frame is smaller. They stick out far from the face to me to. Like Cyclops glasses to me. When I first put them on it immediately noticed how uncomfortable they were compared to my Samsung 3D glasses. My Sharp 844U 80 Inch has a l o t of crosstalk. I don't know if its my model, or other people don't notice it. It's only in background though, the main character or scene looks great, but watching Prometheus for me was horrible at scenes, it was basically like watching the background scenes with no glasses at all, everything was double.
So I decided to get the 20B's (My original plan when I first started looking in 3D glasses) to see if just mmayybee it was the glasses. The 20B's are way more comfortable. The lens is big on it making it feel like REAL glasses. The viewing area just feels larger, and its closer to the face. So wit that being said, the quality seemed a little better, but who knows.
Hope this helps.