>>3201773Probably my EF 50mm f/1.4.
It's not my most used lens in terms of pictures taken (that would be my 85/1.8), but it's my most used lens in terms of what's on my camera body by default most of the time.
I've also got a 24-70 f/2.8, which is more versatile, but it's big and heavy so I rarely actually use it unless I'm in the situation where I can't carry a camera bag, know I'll want to go from wide to short tele, and will be shooting in relatively low light.
Pic related; taken with my 50/1.4.