I'm a little--but only a little--embarrassed to admit I have three 50mm lenses for my Leica M system.
I started with an early Rigid Summicron, which I acquired quite cheaply--it was hazy at first, and had a dodgy aperture ring. For not too much, I was able to get both problems fixed by the legendary Malcolm Taylor.
I grew to love this lens, the way it handled and the way it rendered (except for flare, which is a pretty common problem with most versions of the Summicron), but then my local camera crack dealer offered me a nice Version IV. So I traded in the Rigid on it.
As I missed the lens so much, even though the more modern lens was clearly better at wide apertures, I later acquired from him a very nice indeed later version of the Rigid when it came into his shop. However, when he then pushed on me a handsome 1964 era Summilux at a very reasonable price, I once again divested myself of the Rigid in trade.
However, that lens was so beautiful and I regretted yet again selling it. So later, when the new owner decided to return this very same lens to my dealer (to help pay for the purchase of a WATE), I couldn't help myself. I bought it back, and I don't intend to part with it.
So which one do I use? The Summilux is normally on the front of my M6 0.85. I actually like the look of its classic chrome on the black camera. And in most situations, it works wonderfully.
When I want ultimate sharpness at wide apertures (but don't need the full 1.4), I use the Version IV. And the Rigid normally lives on the front of my M3, for when I want to stroll about in daytime using Sunny F16 and experiencing the tactile and imaging joys of using possibly the most classic Leica combination. (I just make sure I'm careful about shooting contre jour.)
The lens that gets used the least is actually the Version IV, even though it is technically probably the best of the three. But the Nth degree of sharpness isn't usually important to me--I enjoy the process of making photographs as well as looking at them, and the other two lenses are certainly sharp enough. And they're simply more fun to shoot.
So if and when I decide to part with one, it will likely be the newest lens of the trio. But that sort of points up something else--to me, the lenses are like money in the bank (so long as they don't get lost or damaged). By that I mean, as I paid reasonable prices for them, I will be able to get back probably every penny (and maybe more) of what they cost me if I ever go to sell them. And effectively I'll have had the enjoyment of using them for free while they were in my possession.
At least that's how I rationalise it!
