Most of my lockup scenarios are low to medium risk, so I prize portability over security, And for that reason, I use TiGr Locks.
They're unbeatably light and smartly designed to stow easily and unobtrusively on the frame, so I always have it when I have the bike, rather than being something that's kept in a bag, or that dangles irksomely from the bars or seatpost that you wish wasn't there.
I like that the size allows me to capture frame and both wheels. It's a stylish conversation starter, too!
TiGr Lock | Elegant Bike Security