Having tested most of them over several years, roughly by how much they actually did:
Going out at night with a torch: genuinely effective and nobody wants to hear it. Two or three nights in a row, an hour after dark, especially after rain. You will be shocked at the numbers and the difference is immediate. It is the only method that removes them rather than deterring them.
Beer traps: work, with caveats. They do catch a lot. They also attract slugs from beyond your beds, so sunk right among your seedlings they can make things worse locally. Site them at the edges, not in the middle. Emptying them is unpleasant.
Pellets: effective. If you use them, use the iron phosphate type sparingly and according to the packet rather than scattering generously - more is not better and the packet rate works.
Copper tape: works on a pot, useless on a bed. It has to be a complete unbroken ring with nothing bridging it. One leaf touching the ground outside and it is a doorway.
Eggshells, coffee grounds, sand, ash: did nothing measurable for me. They are widely repeated and I would not spend time on them. Ash and grounds also stop working entirely once wet, which is exactly when slugs are out.