I've cycled through five, and for reasons I don't fully understand I seem to have stabilized on the 50 1.4 ZE Zeiss Planar. I'm not sure any of them count as a pro lens, but hey... I'm an amateur so let's roll the tape:
Every single one has had more than one drawback, including my current one, and to be honest I have brought those foibles upon myself
50 1.8 aka the nifty. Everyone should own this lens at some point in their life. Forced myself to use this for three months as my only lens as I tried to figure out how to use a dslr outside of the "green box" of auto. It sounded like someone shaking a box of gravel when I autofocused it. I like the fact that it's featherweight, but it felt pretty cheap... and I didn't like how short the throw was when I selectively focused manually. Gave it to a neighbor kid who was just starting out with a dslr so she could get a feel for a fast prime.
Pentax Super Takumar f/1.4. Loved this lens on my Rebel. Had a weird yellowish cast to it from an old radioactive element which warmed up my photos a touch. It focused like a dream and had a really lovely bokeh. Unfortunately, it hit the mirror on my 5d2 and I sold it essentially out of fear of a nasty repair bill.
Minolta MC Rokkor 50mm f/1.2 (sounds a bit like a rapper, actually). Loved loved loved this lens on my Rebel. It was a nightmare to get it in focus though with that tiny light-stealing viewfinder at 1.2, but when I did (often only though the use of liveview) it had a super dreamy character. Very forgiving for people (providing I was able to get their eyes in focus, never a guaranteed thing...). Like the Super Tak, it hit the mirror on my 5d2 and I needed the money to buy a couple of other vintage beauties: a c/y Zeiss 35mm f/2.8 and the...
Contax/Yachica Zeiss 50mm f/1.4 Planar. To be fair, I didn't really give this one much of a chance. I spent most of the year I owned it with the c/y 35 glued to my camera. When I did pull it out I enjoyed using it. It was pretty beat up on the barrel but still had that Zeiss/Cosina microscope like feeling to it. My biggest beef with it ended up being that I kept missing exposure and missing shots with it having to set focus, then adjust aperture, then meter, then go back and open it up to focus again because I wanted a different composition, then forget to set the aperture and end up with something so damn white hot that it was virtually unrecognizable as a photograph of anything other than a ball of plasma. Sigh. Because of that, I ended up selling both my C/Y zeiss beauties to a videographer and a film enthusiast.
Which leaves me with the Zeiss 50mm f/1.4 ZE Planar. It's wonky, it has some focus shift issues, I have mediocre eyesight so I end up missing focus a bit, I still haven't got it fully dialed in for microfocus adjustment so I can't fully trust the confirmation lights... but it's light, it lets me be very precise when I take my time and set up a shot, and it renders colors beautifully letting me spend more time taking pictures and less time on lightroom.
I should probably come in to the modern age and get a good autofocus 50, but if I'm feeling lazy chances are I will continue to fall back on the walkaround zoom.