Hard tri-fold is the only way to go in my opinion. Can walk/stand on them, put stuff on em, but they fold up easily. Full hard covers basically don't allow you to put anything in the box taller than the bedsides without removing the cover (atv, dirtbike, couch, etc). Soft covers are easy to just cut into, and you can't really put stuff on them (But I'd still take this over a full hard cover).
Hard tri-folds seem to have all the advantages and none of the disadvantages.