I had to make a similar choice a few months back -- the 35L or the new 28 IS. Rented them both first. I ended up choosing the 28 IS and have been quite pleased.
Money didn't factor into this call. My considerations were as follows (apply these to your situation as needed):
The 28 IS (2.8 + 4 stops IS) is more handholdable in low light than the 35L. That applies to what I shoot, but perhaps not for you. (I'm often shooting nighttime street or stationary people indoors at social events.) With my 5D3, I can bring home useable shots from ISO 6400 - 10000 shots at 1/20 of a second. The 35/1.4L cannot bring those shots in without shooting wide open (i.e. soft anywhere but in the center with an unusably small DOF for my needs) and at an even higher ISO to net a useable non-IS shutter speed.
New non-L EF (not EF-S) designs rival old L designs from an IQ perspective. The new 28 is as sharp as the 35L in head to head on the 28's wide open end (comparing both at F/2.8 ). The 35L is a shade better in the corners when you stop it down for landscape work. So I shot both and couldn't really see a difference in the IQ.
IMHO, the 28 IS has better build quality than the 35L. The 28 IS build/materials/etc. is nearly identical to the modern 'plastic' L lenses like the 100L macro (though the 28 lacks a gasket), whereas the 35L is dated, has cheaper looking/feeling plastic, etc. As an owner of the tank-like 24-70 F/2.8L Mk I and 70-200 F/2.8L IS II lenses, I was shocked to see the famous 35L I've heard so much about resemble my non-L 50mm F/1.4 in build quality.
The 28 is small, light, and unassuming. I love this as I often shoot candids, street, etc. In return for this little lens, I lost the prestige of a red ring. Great trade for me, but perhaps not for you.
So, given all of the above, I went with the 28. It was the right call for me. Had the same IQ statements been true and the new 35 F/2 IS was available then, I very well may have gone with that lens instead of the 28. But, if you like what F/1.4 - F/2 looks like, are shooting moving targets (where IS's longer useable shutter speeds won't help you), or need a red ring -- the 35L is the option.
thanks for the info I'm holding out for the 35 f2 IS f2 rather than f2.8 makes a big difference for me and the 1 stop difference from f2 to f1.4 is not as much of a benefit as the 4 stop IS IMO