Rule #1 pick something you like! If you like it, nothing else matters.
....but if you’re torn and trying to decide which one is for you, here are some things to consider:
gemstone vs glass: scroll back a couple posts (or head up to my stories) for all the benefits of using a gemstone set. But why maybe pick a glass set? They’re gorgeous! Really you don’t need any more reason than that.
size: most sets use either 6mm or 8mm beads. This just comes down to personal preference. Here is a quick visual to help you decide:
Don’t get too wrapped up in picking a set - you can also have more than one!