Ultimately, the question of what dice you use is entirely up to you, the player. Some like to match their dice to a certain aesthetic of a character: celestial warlock might choose a deep purple veined set, for instance, or a bubblegum princess the brightest candy pink. But when it comes to the material, there's a bit of debate around whether plastic or metal is better for the table. Let's look at some pros and cons.

The first pro of metal dice is that they tend to be a little more durable. Not only do you get a thoroughly satisfying sound when you roll them (who doesn't like a crit with a little style?), but you also may be able to use them for longer than your typical plastic polymer dice. They keep their form through more rolls, and therefore keep balance much longer, particularly when they're well cared for. I'm not saying that you need to store each metal set in their own velvet lined wooden box, but keep them separated from plastic to avoid damaging the softer dice, and away from moisture to avoid oxidation.

The cons really boil down to price. A great set might last a long time, but you're not likely to find them for cheap. Metal dice cost more to produce, and you can be sure to see that cost reflected in the price tag. You may not be able to have as many metal sets, and they can be difficult to store separately, which is inconvenient if you need to carry more than one set like I do for my sessions. Not to mention, metal dice, by virtue of being heavier, are capable of damaging wood and tile, so flimsy furniture and accidental drops to the floor could have consequences on par with a nat 1.