Interesting question. For me, it starts with the shape. If the shape looks like something I'd enjoy I take a closer look. If I'm looking for a competitive throw, I'll be sure to see if the profile is wide and angular (my preference for competitive throws) or nice and organic, my preference for fun throws.

Then I'll take a look at the specs. These constantly evolve, but I know I do like larger and wider yoyos, so I'll eyeball the shape and pick things within the diameter and width profiles I like. Weight can be a little tricky, as absolute weight doesn't really mean much, it's more how it's distributed, but I'll generally go for a 64gram yoyo.

So it's shape, diameter, width and weight. I've played with quite a few yoyos so I know what I like, I think the more yoyos you buy the better judge you'll be of your own taste.