Apple’s Notes app isn’t the only player in the note-taking field, not by a longshot. Evernote’s OS X app lets you choose a default font and size for new notes, and also offers much simpler ...

Tap "Notes." A list of fonts appears. Tap the name of a font to select it, such as "Helvetica." Press the "Home" button, then tap the "Notes" icon to use the app with the newly designated font.