I always secure my bike to something solid and immovable, like a decent bike rack or lamp post, though a pile of bikes all locked together would do if I had no option. I wouldn't trust it if it could be carried away, no matter how noisy an alarm was.
I use an
Abus Granit Extreme.
I also have an
Abus disc lock and chain adjusted to form a loose noose at one end and a tight locked noose at the other end.
I also have an
Abus Granit Quick 37 with an
Oxford Monster 14mm chain.
Over kill and over weight perhaps

but I can select one, or two, to take depending on need. (I originally got that lot when I had a costly motorbike, hence my user name. Motorbike then sold and a workshop built with the proceeds.)
With some of my bikes losing the lock would be a bigger financial hit then losing the bike!
Often I just have a cheap and light weight 4 digit combination cable lock fed through the wheels and frame and around something solid, and also a cheap D lock for speed, and I keep the bike in sight.