Serpentine belts are used in new vehicles due to the fact that they are easier to maintain and are less complicated to install. V-belts are still used on the majority of the older, classic motors. Some simply like the style they give or having each of their accessories run on their own belt.
The deep V of the v-belt can help guide the belt back into place if the alignment is slightly off. And with being a smaller size belt, the pulleys tend to be on the smaller side making things a little more compact. They can be used in any orientation, vertical, horizontal, etc. but they can’t handle the higher RPM’s and cannot be used for long distances because of the weight per unit of length. And if one belt does end up slipping off, the others could keep your engine going for a short amount of time until that first belt causes the others to slip as well. Not to mention that the location of the accessories and pulley’s gets to be pretty complicated on most engines making it more of a hassle to change the belts when needed.
The thicker multi-rib design of the serpentine belt provides a better belt-to-pulley contact ratio that creates less slippage. Most serpentine systems being a one belt system, there is less distance between the accessories simplifying the engine compartment. They use proper tension with the help of a tensioner and tend to be easier to modify because you only have to remove the one belt. The main downside if you do decide to do a serpentine conversion is the brackets and pulleys need to be made for your specific engine model. It’s not a one size fits most kind of style. Which can be annoying but that means the engine in your car could very well be one of a kind.
Both of these are good in their own way. Not one is truly better than the other. What it comes down to is your preference and what style you are trying to go for. If you are looking to do something more on the interesting side and want to make people think how in the world you did that, or you want to keep the original style and you’re not afraid of a little extra maintenance work then v-belt would be your way to go. But if you’re looking for something new and that offers a little more. Something that is also on the easier side to maintain, a serpentine belt is what should be going onto your engine.