Looking for iCloud note-taking app
You should expand your requirement to iCloud and Dropbox for following reasons.


iCloud is sandboxed to only certain apps. In other words, any notes an app X creates cannot be read and modified by app Y. Dropbox allows any apps that supports Dropbox to access your notes. You may like app X now but you may want app Y later.
iCloud syncing can be useful if you have multiple iOS devices, for things like settings and miscellaneous data (e.g., scratchpad).


I have tried over a dozen note taking apps that syncs over the cloud. The app that I keep going back to is Elements (http://www.secondgearsoftware.com/elements/). It has very clean yet functional UI and frigging fast.

I do have few wish list items though: (1) tagging and/or support for moving notes to different folder, (2) hide certain Dropbox folders (I linked to the root folder), (3) default font setting (Museo Sans is very pleasant but may not be for everyone), and (4) Markdown keyboard (it fully supports Markdown but I don't remember all the syntax).