Dear Dave,

I've owned & used all the cameras you list (still have some, including a IIIa, though no Canons for years) and I'd go for the Bessa-R for sheer usability. Old Leicas have terrible viewfinders -- arguably worse than the Zorkii -- and old Canons are well, old. There's a great pleasure in a good, old camera but a lot less when it needs repairs.

But bear in mind Claire's advice too, possibly with a new accessory viewfinder.