Looks like I'm late to the party on this one, but a few thoughts.
For me, the ones that stand out are the ones that make me believe that they're a miniature tree. One that I could imagine standing next to as a miniature person, that I could picture sitting underneath and having a picnic. The also-rans all generally have some element that breaks the illusion of scale, whether it's the wrong pot, poor nebari, out of scale branches or leaves, overly manicured look, picasso-level jin and shari, etc.
I can appreciate the more traditional styles for what they are, and especially all the work that goes into them, but the ones that always stand out are the ones that really make me feel like I'm in the scene.
I said this in another forum recently, but it definitely applies here. Nature is my final arbiter of what makes a good tree. I study actual trees every chance I get, and I draw inspiration from the beauty and structure I see in real-life trees. For me, the best bonsai reflect that natural beauty, and make me believe that this tree could have feasibly grown on its own in nature somewhere.
Even when I acquire new, less refined material, my strategy is to look for things that I believe have the potential to be refined into a natural-looking, miniature tree over time. If it doesn't, it's generally an automatic pass.
The way I develop my trees reflects all of this. I tend to set them on a particular path with the initial styling, and then gradually just let them grow out and scale up. During this process, I'll balance prune occasionally to keep things moving in the direction I want, but I mostly just leave the tree to it's own devices, with occasional interventions to keep things interesting. As I intervene, it's generally all about adding elements of age and character through wiring and pruning, with the intent of making what's there look like it could have happened on a full-scale tree over a period of many years. For me, it's far less about the formal rules than it is about answering the one burning question: Could this feature on this tree have plausibly happened in nature?