Most popular gearing set-up

Wow. that is an open ended question. Do you mean for me, here in Rome, or you... wherever? 🙄

Having ranted, I would say that a lot of people ride 53or52x39s OR compacts 50x36or34s up front and whatever gearing came with their bike out back, which would probably be a 13x26 or something similar. And we are not even talking about triple cranks...

It really depends on where you ride, what shape you are in, how mechanically inclined you are (do you have multiple cassettes and swap them depending on rides) etc etc etc...

Personally I ride a 53x39 up front and 13x26 in the back. I also own a 13x29 for mountain vacations (and hope one day to be able to purchase a use an 11x23, but am not holding my breath).

Hope this helps.

It really ends up being a choice among the options offered by the manufacturer of your components. I think you choose the bottom and top ends and the rest pretty much falls into place. I happen to ride the same setup as Powerful Pete (53/39; 13/26). I don't have any climbs >8% and my 39/26 gives me a high enough cadence at my climbing power. I gear out on descents with my 53/13, but that's not important to me at the moment. When I start racing next Spring, I'll get a different cassette (12 or 11) so I can keep up on fast descents. If I had climbs >8%, I'd get a cassette with at least a 27.