I got the Summicron. It's a great lens. I have a ton of pictures of it on my flickr stream; look in my tags. The 28/2.8 ASPH looks like a great lens too. Small and almost cheap by Leica standards.
I'm sure the Hex is a good lens, but the prices of them have just gotten too high in the last couple years. About 4 years ago, you could pick up a Hex 50 for about $300 and it was a great bargain. For 500-600, I'd rather just get a new Zeiss. If the 28 Hex is going for $700-900, either get the 28/2.8 ASPH for not that much more or save up for the Summicron. You can get Summicrons for a hair over $2k if you look.
After I got my Summicron, I ended up buying a VC 28/3.5 to complement it. Cheap and tiny. It's a great lens. Perfect for a day out in good light when you just want your camera to be small. That's the lens I'd really recommend getting even if you already have a Summicron. Even if it weren't cheap and tiny, it'd be highly recommended.
