I have to vote for the 50mm f1.4.
Better build, including a metal bayonet mount (instead of plastic). USM (although the old motor type) is quieter and quicker. 8-bladed aperture (as opposed to 5-bladed) for nicer background blur. Better flare control and richer color rendition. Sharper corners.
Not that the 50/1.8 is a bad lens. At it's price, it's definitely a bargain. But, for me, the 50/1.4 at a little higher price was a better choice.
50/1.4 should always be used with a lens hood, too. So be sure to get that accessory... It's worth the little bit extra. The hood is not only helpful when shooting, it also protects the somewhat fragile auto focus mechanism against bumps when reversed on the lens for storage.
The AF of the 50/1.4 is it's weak point. It's quick enough, quiet enough, accurate and allows for full time manual focusing... But it can be damaged with a hard rap on the focus ring (thus keep the hood reversed on it when stored). Some say it wears out more quickly with a lot of manual focusing. But I bought my lens 8 years ago, and it was already used. I'm not certain how old it actually is. It hasn't gotten any special treatment, either. And, knock on wood, it keeps on working fine.
I'd like to try the Sigma 50/1.4 and compare it, in spite of some reports of issues with focus calibration (my cameras have micro adjust, or it can be sent to Sigma for calibration). The Sigma appears to have, if anything, even nicer bokeh. The Canon is slightly soft wide open, which quickly reduces as you stop down and is gone by f2.8. Reportedly, the Sigma is the opposite... Sharp wide open, but less so beyond f8. I tend to use this lens at larger apertures, so the Sigma sounded ideal... But, unfortunately it's more expensive, a lot larger and significantly heavier. Those are reasons I haven't opted for the Canon 50/1.2L, either (a lovely lens, but more than I need in many ways).
The Canon 50/1.4 is overdue for an update to it's auto focus mechanism, and perhaps some other minor revisions. But, it's already a good quality lens. Some years ago Canon refered to it as their "reference" lens, which was the basis for the specifications of all the other lenses in their system: color rendition, sharpness, performance, etc. It only took me a few minutes handling it and the EF 50/1.8 side by side to make up my mind. Plus, I own and have used these two lenses in the older Canon FD-N versions, where they are similarly positioned (entry level and mid-grade, I'd call it).
Note: there is an older EF 50/1.8, the original one, that has a metal bayonet mount. They can be found used, but tend to sell for as much as twice what a new Mark II with the plastic bayonet will cost you. And, they are getting pretty old now... The Mark II replaced it in 1990!
Now, on your camera a 50mm is going to be a slight telephoto, instead of a "standard" lens. I use it on 1.6X, primarily, where it's even more of a telephoto and very useful as a short portrait lens. I don't have a 1.3X camera like yours and 50mm isn't my favorite focal length on a full frame... This is just a personal preference, though.