I'm surprised nobody's mentioned this.
Use one of those EXIF analyzer tools to figure out what focal length you use the most. Buy the lens closest to that focal length.
And, as others have mentioned, the Sigma 35 and the Canon 50 f/1.4 both deserve serious consideration. Don't automatically assume that the Canon red ring means it's the best lens, or especially the best lens for your purposes. The red ring generally means it's a very good lens...but, in the case of the 50s, the 50 f/1.4 is 90% as good as the L at a quarter of the price, giving the f/1.4 perhaps the best price : performance ratio in Canon's lineup and the L the worst. If that last 10% means something to you and is worth a thousand bucks (and you can afford it), by all means, go for it. Just go for it with your eyes open.
And the Sigma really does appear, by every account I've come across so far, to be marginally better than the Canon in pretty much every way that matters. Not enough better to warrant selling the Canon (unless you're desperate for cash), but certainly enough better to warrant buying the Sigma instead. Some are worried about future compatibility citing some infamous past problems, but with that USB dock that's also a non-issue. Long-term resale value might still be a concern, but that's a moot point if you buy your lenses to use for photography as opposed to financial investment instruments.