Best for me.

I like it because it highlights the word that you search for. No need to scroll through the text. And if it finds more searched words it will direct you to the next hit. Systemic Notepad cannot do it. And thats where I need short notes - search my notes quickly.
But it works only on iPad or iPhone. In MacOS you need to use the Cmd+F in Safari (after login to the Simplenote.com). Native Simplenote for MacOS cant do it. So I should give 4*. But I like this app. Install!

petriwoj about Simplenote, v4.3.3