I would say that it depends on what you are using it for. The #168 is great for contouring on the face, but not very large, so time consuming for the body.
The #174 is fairly ginormous. Ok for face, great for body. The #174 has much looser fibres, for a softer build/blend of colours. The #174 is a Pro brush (but occasionally pops up at CCOs).
The 168 is
much less expensive. There is talk that the #168 will be discontinued shortly.
Hope that helps.