I find it depends on the space and density of the crowd. That often dictates how close I get to people. The closer I'll be, the wider the ideal lens up to about 21mm. Or at times I go with a 100mm and try to focus on layers rather than isolation.

I love TLRs as well but recently have been using rangefinders and folders more frequently on the street. The odder looking the folder, the more likely people will either ignore you or view you as some sort of eccentric which seems to put them slightly at ease in the same way a TLR does. I go with rangefinders because they're compact, I can take a couple of lenses in a small bag and people seem less intimidated by them than a large SLR.