The V requires a bit less precision in alignment, and is very effective for each inch of width, but a single row probably isn't enough for safety and positive drive at high boost. If you run multiples, try to get the same brand and series (not just the length) to be sure of equal tension. Due to the wedging action it needs slightly less pre-load than a flat belt.
A serpentine is easy to adapt since the same profile is used on many modern accessory drives, but the lateral alignment (front to rear) is more critical, and the shaft parallel also - anything that allows the shaft to bend or flex will jump a serpentine off, and it may be badly damaged by riding over the end flange. It looks safe to run a 6-rib belt on an 8-rib pulley as long as the ribs align, which gives you some design freedom.
