simplified, but decently designed UI
setting to show uncropped images/videos in posts and comment view
dark mode (adaptive colors syncing with device theme and color palette are a nice to have, but not mandatory)
shortcuts to formatting options in Editor (list, bold, italic, code, citation, etc.)
color setting to highlight OP or self in comments, links and other stuff for better information parsing
feature to easily minimize comment threads

Sure there are a few that satisfy some or all of these, but you have to take into account personal taste as well. No one will buy a banana with perfect nutritional values, when it tastes like tobacco.

There isn't a one-fits-all solution, just try them out and stick with what fits you best.

For now I completed the client speedrun and chose Sync, but I'll give Boost a try when it releases, since I used them before, but as soon as Infinity hits the store, I'll probably return to that, Docile Alligator created the perfect mix of simplicity, usability and visibility for me.