Originally posted by Igilligan LOL
Okay, the Canon 1.8 is sharp, and a very decent lens, but the build quality makes it feel like a toy lens. Still, some of my friends who shoot Canon love it, and for the price, it is almost an automatic buy for any Canon shooter who doesn't want to pay ~$350-400 for the 1.4.
The FA 50mm 1.4 is a very nice lens. It was a great deal when it was under $200, and the current price is fair, if not exactly lba inducing. It is very comparable to other company's 1.4 50's in pretty much every way (read the various reviews). My copy of the lens is as sharp as the other system's 1.4 50mm lenses (that I have used, Canon and Nikon) at all apertures. It is a very good lens with one significant flaw (purple fringing at wide apertures in high contrast situations). Still, taking all characteristics into consideration, it is as good as the competition.
The Pentax AF 50mm 1.7 lenses (unfortunately discontinued) are great. Extremely sharp and sharp even wide open, only a bit slower than the 1.4, but the bokeh stopped down isn't that great unless you like pentagons. The price on the used market is also not too bad (granted, it is still more expensive than the Canon 1.8 new with warranty).
So if you are looking for a less expensive autofocus fast fifty, I once again recommend the 1.7. But, if you find the 1.4 at a good price, don't pass it up, it is also a very good lens and has a few advantages over the 1.7 (speed, bokeh,...1.4 bragging rights...lol).