Looking for a wide lens around $500, which do you prefer?

17-40 is the easiest option but the edges are a little soft on full frame. Voigtlander is interesting - I have their Leica M 21 F4 and it is a great lens - much sharper than my much more expensive Canons (e.g. 17 F4 TS). However, their design for an SLR is unlikely to perform as well as their rangefinder lenses. I suggest you test them and see if you prefer the zoom flexibility but soft edges to the Voigtlander size, build but MF nature

Well, obviously the 17-40 is more flexible and is a very good lens. Much wider on the 5Dmk2. I think you are not comparing apples and oranges with 2 primes in there.
What lenses do you have now and what are you trying to accomplish?

I don't really care about "zoom". I prefer primes. The 17-40 is an option because it is priced well and is considered to be very sharp. It's also the 1 of the 3 listed I have use before. #1 reason I shy away from this one is that it is so big. I am a little nervous about not having AF with the Voigtlander, but I lean towards this one. I like the solid build quality, and the fact that it is so small.

All I own right now is the Canon 50 1.4, and I love it, but it is way too long for my APS-C chip. I use it for portraits... beyond that I have to borrow. I have used the 24-70 L as well. I just don't care for the full-range zooms at all, and I will not consider floating aperture lenses or crop sensor only lenses.

I also might trade in my 30D for an original 5D at some point if I can find one for a fair price. That would solve some of my problems. If I did that, I'd have to consider the Canon 28mm USM. I don't necessarily need an ultra-wide, just a wide. My thinking with the 20 is that it's at least useful for either format.

I am a digital guy in the ad industry. I don't shoot for a living, and I've lost touch why I originally got into this. I'm trying to enable myself to take more pictures!

I know you said $500, but you then included a $700 lens, my thought is to save a couple of hundred extra and get a secondhand 24 f1.4 L MkI, these can be had regularly for $900-$950.

My reasoning is simple. It might be old but it is a high quality lens, it has very good AF, it will give you the best options for DOF control, something you might want for portraits and not easy with crop cameras and slow wide angles, also it was built for FF. If you don't like it you can resell it for the same money you paid for it, even in a years time.

Sigma make 24/1.8 and 28/1.8. They're full-frame lenses. They're known for nice bokeh, sloooow AF (think of it like MF lens with a motor in case of emergency), low price (especially used), and they're built like battle tanks (heavy). I think the close focusing distance is quite short. The 28 mm is reportedly a tad sharper than the 24 mm.

Sigma also makes a 20/1.8 which is supposedly less sharp than the other two. Voigtlander 20/3.5 supposely has sort corners as well.
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The 24mm L is interesting. I'll keep an eye out for an older one. I'm a big fan of old stuff in perfect working order for a great deal.

Nate,

You are spoiled for choice, well you will be soon, with the announcement of the two new 24 and 28 f2.8 primes with IS. $800 for the 24, $750 for the 28.

I would pick the older 24mm f/1.4 L over the new (not yet available) 24mm and 28mm. It would be nice to try them side by side, but I'd try the 24mm L and see how I like it.

Very cool. Where's Canon's counter to the Nikon D800? That's what I want to know. If there isn't one, maybe I'll be switching.