I like locks to be easy to use and not too much hassle.
Currently, I regularly use:
- Abus 5950 NR frame locks permanently fixed to 3 of my heavier bikes and the two visitor bikes. 5950 NR is a relatively high-end model.
- an Abus Granit Plus 470/150HB U-lock. Once again a relatively high-end model, but not as heavy and bulky as the most secure U-locks.
- a length of chain with an Abus 20/70 padlock. This one is usually "either/or" with the U-lock above, but if I think the theft risk is important I do occasionally take both.
For convenience, all the above use the same key. I carry one with my set of house keys and have a second key in my tool kit, which goes with me in my "valuables" bag if I leave the bike locked up.
I also have the Abus cable Cobra 10/200 2 metres, which is useful for attaching two bikes together or for securing one bike to a large-diameter object, or threading through as many bits as possible.
Finally; I have a small and light cable lock dating from the 1970’s, this has a different key. Same principle, one with my set of house keys and a copy in my tool kit.
My wife's two large wheel bikes have permanently fixed Abus frame locks, but not with the same keys as mine.
My two lightweight bikes and the three family Bromptons don't have frame locks. In general, I don't leave these locked up for any length of time, but carry the little cable lock for the inevitable short stops. And I try to keep the bike in sight as well. If I use a Brompton, the folded bike usually goes with me (into meetings, medical appointments, etc).
There are exceptions. If I have a long day trip with little luggage and a planned stop where I have to leave a bike outside I will sometimes use a lightweight bike. And sometimes we use the Bromptons for holidays, so need to lock them up for food shopping, etc. In these cases I add the U-lock, Abus cable and/or chain/padlock as I think necessary.
My little cable lock is also useful for locking pannier bags to the rack or frame, and I use it regularly for this purpose on my touring and utility bikes.