V-belt is cheaper and lasts longer,
Are you sure? I've never had to replace a serpentine yet. But I've seen allot of V-belts come & go.

serpentine belts bend both ways,
multi-rib belts I haven't seen much of, but I think they're a lot like
serpentine.
Multi-rib & serpentine are the same animal, I believe. Multi-rib refers to the belt design, but the belts can vary in length. I'm using a short multi-rib belt for my alternator only, but if it was longer and was used to go around my alternator, water pump, idler pulley, power steering pump, A/C compressor, etc, then it would be called a serpentine belt. But the term is often used interchangeably.

    At least that's my take on it. I could be wrong.

Todd