I own a couple of these, and like them. Also have the Summar and a nice Summitar, so I can compare a bit. Haven't used the Serenar wide open, and not for some time, but I was happy with the results. The Leica glass is also very interesting, but may be more expensive and problematic. I would think either the Canon or the Summitar would be a good choice for a first lens, with possibly a Summar as a future purchase. They are different, and Raid has an excellent series of shots of his ever patient daughter that shows many of the characteristics you are looking for in a lens. Another good idea might be a nice FSU that has had the back focus properly shimmed. Brian Sweeney did several of these lenses, and most turned out to be very nice.
Lots of choices in 50's, as you can read here in several places.
Harry