Cons: It's almost too simple. Simplenote allows no formatting of any type and does not support Markdown editing, so if you want to style your text at all, you are limited to bullet points, numbering, and capitalizations. This sounded great in theory but I've noticed if I can't bold some text or make section headings bigger in my notes then I frequently lose my place while teaching and preaching because all the text looks the same. Tagging is great, and if tagging is your thing, you're going to love this app. If it's not, stay away, because that's the only amount of organization you get from Simplenote. All you have is a long running list of your notes, in order of what was last edited first. There's the option to 'Pin to Top' which comes in very handy.
I've run into some sync issues (as late as Oct-Nov 2013), but most of those seem to have been ironed out. The apps still crash on me frequently (once to twice a week) - I don't think a day or two goes by that the Mac app hasn't quit for no apparent reason and once the iPad app crashed on me while scrolling and preaching in front of hundreds of people (ack!). The iPhone app has a bad bug where it will crash when trying to sort changes in a note. I know developers are active on this app and I love Simplenote, I just cannot afford to use something that's unreliable. If the apps were stable enough, I might have this as my go-to platform.
Plain Text
And here we are, talking about the joys of plain text once again. I really don't know why I migrated away from plain text, but it seems that my search has brought me full circle, back to where I started.
You may read this and discount the plain text preference as an uber-nerd thing, but, in fact, it's really not. It just works.
Pros: You can use a variety of text editors on all devices and plain text formats, including regular ol' .txt, Markdown, or Multi-Markdown. Markdown allows you to style your text how you want without changing to rich-text format. It uses simple symbols like asterisks to indicate bold and italics and hashtags to indicate headlines. Comes in handy when you get it down. The app I love to use on the iPad is Editorial, and on the Mac it's Byword. You can usually sync these apps to Dropbox and keep them in nested folders, easily categorizing what you need where you need it. Apps like Editorial, Nebulous Notes, and Byword are minimalistic and usually offer inline Markdown support, so you can see your bold and italics and headlines while writing. Best of all, plain text is future proof and my files are not tied to any platform, so I can move them around as I please.