Canon 35 f/2 vs 50 f/1.4

There's not guarantee any lens will be perfect out of the box, but yes you hear more QA issues with Sigma lenses. If that is a huge worry, then the 35/2 is certainly a good little lens. 28mm f1.8 would focus more quickly and quietly if you care about the USM/HSM.

That said, the Sigma 30 is really good and odds are very much in your favor to get a good one. It comes with a 4 year warranty vs 1 year on the CAnons, so if something isn't right you can certainly get it fixed.

Sigma 30mm @ f1.8

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Sigma 30mm f/1.4, performs better wide open, is faster, better focal length for a crop, even 35mm is a little long on a crop, HSM focus motor, comes with case and hood included (not optional extras $$$). Only critisim I could level at it is the MFD is not a close as i'd like.

No reason not to look at third party, in the normal prime market for crop cameras Sigma seems to be the way to go. Another option thats often overlooked is Tokina's 35mm f/2.8 macro. Its a little slow but then I suppose if you decided later you want a standard zoom at f/2.8 this lens would still be useful as a proper 1:1 macro. Not much info around about it though.

Of the 2 you listed the 35 f/2 would appear to be the better length and most reliable (on tuesday alone we had 2 thread here documenting focus failures with the 50 1.4)

Some of the judgments I read here are subjective, like the ideal focal length for a "normal" view on a crop. Personally, I like a "little longer" on my crop.
The 35f2 may be sharper than the Sigma 30f1.4 at f2, but sample variation probably plays a role. The 35f1.4 is much sharper than either at larger apertures, but the 35f2 does very well at smaller ones:
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When I got my copy, it was $200 less than the Sigma. I didn't want the extra cost, and didn't think it was worth it - I would rather shoot at smaller apertures than f1.4. At current prices, the Sigma is 50% more than the Canon - and I prefer the longer focal length of the Canon - for my purposes.
The Canon 35f2 is sharp corner to corner stopped down, and very good wide open. It does what I want a "normal" lens to do on my crop. When I used a 45f2 on film, I always wanted longer when getting candids of people indoors in natural light.