For the last few months, I've been walking around with a 50, a 35, 28 and 90. And the leica, of course. But the 50 - a nokton 1.5 asph II M.C. - rarely leaves the camera. The few times I screwed on the 35 I had a hard time judging the frame. It feels not quite wide enough, but there"s more than I want in the frame. And I only fish out the 90 when I am already too far away from my subject, the results are so-so.
Coincidentally, I'm also going on a short trip, and this lovely thread has me reconsidering which lenses to take along. The Nokton of course. I'll take the Summitar, for when I absolutely want swirly bokeh and creamy sharpness. The 28 Ultron for when I can't step back far enough, and the 90 for when I'll fall off if I get any closer. The last 3 will probably never come out of the bag. But it is better to have the option than to want it.
Seems to me, this is a decent distribution of focal lengths : 28,50,90. Switching the 90 for a 15 could be interesting, but I don't have that. Not sure I want to invest in a super-wide I might never use.
Here ends my entirely irrelevant opinion.