I always use 2 locks when I have to lock up outside. I use a kryptonite U-lock and a cable lock as extra security. Don’t forget to lock up both wheels. All locks can be broken, but having 2 different kinds on one bike makes for a great deterrent. The only way to ensure that your bike does not get stolen is to keep it inside with you, and even that doesn’t work 100% of the time. Also, I tend to use locks that have keys instead of a combination. I have had combo locks that spontaneously change combinations on me, preventing me from unlocking my bike (although I blame myself for that). The downside of keys is that you can lose them.
For a U-lock, I recommend the New York Lock
And for a really heavy duty chain lock, I like the New York Fahgettaboudit
Any thick cable lock would be a fine addition for that rear wheel.