Initially, I purchased and mounted a big U-lock onto my bike, in addition to a steel folding lock and a cable I keep under my seat.
After riding around for a while with the U-lock, I decided it was in the way too much…..have to swing it to the side whenever removing the battery, and it was in the way when I mounted my bike to my car rack and my maintenance stand.
I live in a pretty nice area, more of a rural/suburban feel, and I’m unlikely to leave the bike unattended for long. I therefore decided to ditch the U-lock, and just keep the folding lock and my cable with me at all times.
If I ever go somewhere where I anticipate having to be away from the bike for a while, especially in a sketchier area, I’ll just toss the U-lock in my rear cargo bag, and bring it along.