what type of insulation for un conditioned attic
Vapor barrier, if any, on the warm side of the insulation.
Type of insulation is your choice. More is better, within reason. Costs vary - if you have space for it, cellulose is usually the best bang for the buck. The insulations that perform better in thinner sections also cost more per applied R-value. With a wall application, cellulose would need a net, or a second (non-structural) wall to hold it in place.