It’s a huge can of worms, and depends very much on the vehicle in question.
But basically, don’t skimp on the quality of the bags. Cheap bags are cheap for a reason. I generally only use slam specialities or certain universal air models. Airlift are actually pretty poor.
Personally I don’t like the ‘new generation’ of all in one digital manifolds/management. They’re massively unreliable and not user serviceable. I prefer 1pc electromechanical ones like the ridetech big red. They’re easily user serviceable and seem to go wrong less in the first place anyway.
The other thing is easily 95% of people just don’t know what they’re doing when actually installing bags. I’ve actually redone more of other people’s installs than I have done fresh installs. I’ve seen airlift and similar bracket kits that install bags incorrectly and/or in the wrong application, leading to premature failure, especially on the rear of fwd cars. And don’t even get me started on some of the ‘big name’ installers in the UK and the shower of curse word that is their work....