I think neither.
50 f1.4 - From using both the 1.8 and 1.4, I found that they are both tack sharp for portraits. And if MTF charts is your thing:
As you can see, they are about the same at f1.8.
Unless you have a bad copy, keep using your 50, buying a newer one is redundant.
40 f2.8 - This is a great lens, super sharp on APS-C. I used it as a standard lens for a 60D. But the focal range is too similar to the 50 you already own, I can't imagine you switching from your 50 to 40 just to get a wider shot.
Canon 35 f2 and the newer f2IS - Canon doesn't seem to do very well in the standard-lens-for-cropped-sensor range. The 35 is ancient and the newer IS version gets owned by sigma. If you really really wanted an excellent prime, the sigma 35mm f1.4 is the way to go for $900.
I would actually recommend upgrading your zooms. If you take a lot of full body shots, then the tamron 24-70 f2.8, eventually upgrade to full frame of course.
Or if you do a lot of headshots and nature stuff, tamron 70-200 f2.8.