Lots of great advice already, so I'll just add this:
I have both lenses(with 5Dmk2), but I've never used the 24mm II for portraits. In fact I bought that lens primarily for video (because of close infinity focus, useful FOV, and of course f/1.4), as well as, to have a 35mm equivalent on my secondary body (7D).
For portraits and wedding work, I use 35mm 70% of the time, 50mm another 25%, and longer lenses (which includes the 85 f/1.2 and up) only 5% of the time.
Long story short, if you're only buying 1 lens, 35mm will definitely give you most bang for the buck.