It depends on your budget like you mentioned. If you completely need to stay within your budget, then you can't go wrong with the Canon 35/2. It is small and compact and delivers excellent sharp images wide open. If you're only going to shoot outdoors in bright lighting, go for the Leica Summaron 35/3.5. That lens is clinically sharp wide open. And both lenses do wonders with B&W images.
If you totally want to blow your budget, go for the Canon 35/1.5. You can get lucky and get it for about double of your budget, but you'll never need any other 35mm haha
I wrote about it on the Canon thread as well. It is an amazing lens with beautiful vintage bokeh and sharpness/image quality that rivals the Leica 35mm's Pre Aspherical Summilux. It only loses when you start comparing to the modern Summilux.
It all depends on the look you are trying to get too.
The 35/2 gives you modern bokeh when you can get it, and is a great overall lens.
The 35/3.5 gives a hint of vintage bokeh, but is mostly for street/landscapes.
The 35/1.5 gives beautiful vintage bokeh, and is an excellent everyday lens.
Here is a sample with the 35mm f1.5
Leica M240 + Canon 35mm f1.5 LTM by
Alex Aguilera, on Flickr
Here is a sample with the Canon 35mm f2
Leica M240 + Canon 35mm f2 LTM by
Alex Aguilera, on Flickr
Here is a sample with Summaron 35mm f3.5
Leica M240 + Summaron 3.5cm F3.5 by
Alex Aguilera, on Flickr