As many mentioned, there are many choices out there, most of which are good, albeit in different ways.
I'll put a plug in for the last pre-asph Summicron (yes, it's the proverbial recommendation of the "lens I have", though I have to say that I tried many before choosing that particular one).
Not the very sharpest or fastest or cheapest out there, but it does hit a sweet point in all parameters: especially size, weight & ergonomics work very well. It's also very flare resistant (very important for me).
While you could hardly do wrong getting almost any of the lenses mentioned if they come up at a good price, the "Summicron IV pre-asph" does pretty much everything well.