For me personally the perfect app just needs to stay out of my way most of the time. My lists are typically what I want to get done today or at most this week - I don't need reminders or nagging, repeated items, subtasks, fancy formatting or complex UIs. Just a list that I can bring up quickly and hide even more quickly.
The one thing that's missing for me right now (and I can see you're already on the case) is an iOS app with iCloud sync. When that's available I could definitely see myself replacing Apple Notes with this.
On a side note (sorry, couldn't help it) I was browsing through the other apps you have listed in the footer and some really nice looking apps in there! Nice work! Definitely going to give TeaCode, ScreenFocus and Expressions a try.