Since I've started to play double bass, my favourite sound was gut strings.
I mean Paul Chambers, Slam Stewart, Jimmy Blanton, Red Callander, Sam Jones, Scott Lafaro; even Ray Brown and NHOP at their beginnings or Carlos Henriquez nowadays
The problem today is to find good quality gut string to a reasonable price.
Lenzner was the solution for me.
And every double bass player I've met fell in love of the sound of the strings and the playbility.
It may not have such big sustain as the metal one but I believe that helps you to improve your technique to get a bigger sound
And you can play any style, even tho their meant to be for classical music, I find them fantastic for jazz, balkan, blues and/or tango.
The bow flows lovely