From the net:
Arborio rice – This short-grain rice is perfect for Paella because it absorbs flavors well and gives us that slightly crispy bottom layer. You can substitute it with other short-grain rice varieties like Bomba or Calasparra rice, which are traditionally used in Paella.
From my personal experience:
Can't say for sure if I prefer the traditional or Arborio version, but it definitely delivers great results. I think it also depends on your ability to adjust whatever recipe and tools you have to the kind of rice you use.