Are vertical or horizontal scratchers better?

Depends on the individual cat. Cornell flags orientation preference as a real factor: some cats are vertical scratchers (up the couch arm, up the door frame), some are horizontal (on the rug, on a flat cardboard pad). Watch where she’s currently scratching to know which type she prefers. Most multi-room households end up needing one of each because most cats have a primary preference but use both occasionally. A horizontal cardboard scratcher costs almost nothing and lets you find out fast which kind she actually uses.