Washers/bushings or bearings?

[Teofilo]

For me, knives' pivot should be made with ball bearings. That's me. The disadvantage of this type is maintenance, and  the higher cost of the knife.
What say you guys?

[Sea Monster]

I'm perfectly happy with a knife pivot made with a bushing (I'm not sure how washers are related, other that to provide a bit of lateral strength - the pivot mechanism doesn't change. At least not before my morning coffee it doesn't)

Ball bearings in a knife pivot is a gimmick as far as I'm concerned. You can't (trust me, you can't) open your knife so fast and so often that there is any real benefit to the design.

Bronze, fibre, or polymer bushes are more than sufficient for any knife pivot, if indeed you need more than the surfaces of the pin and hole in the blade at all.

As you identified yourself, ball bearings will need cleaning - otherwise any gunk they gets in there will either
A. Stay in there and chew out the bearing components, your blade, or your handle.
B. Sieze up the bearing, and then your balls will chew out the bearing components, your blade, or your handle.