Well, talking with my personal experience I've found BlueSerial Beta is the best app for Android devices. It's very simple to use, just connect via bluetooth and you are sorted. You can get reading from different sensors and send commands to control things.
One more thing I liked about this app is that, it doesn't get your privet informations. For example: your phone status, media files, connection to your wifi and all those bullshit that some apps ask for.
It makes me very angry when an app ask for permission of something that is not relevant, like asking for permission of getting call status when I just use the app for Arduino serial communication. I don't get that! Unless they trying to get your info and do business with it.
Anyway this app doesn't require that kind of permissions.