¿What app do you recommend to use with an iPhone for just personal MP3 listening/playback_
I still love iTunes for general listening, but for performance, I have a paid app called "Anytune Pro+" - it's awesome ... tempo/pitch change, and the option to have a track NOT advance automatically. Works great ... even better on iPad because it shows lyrics/chords if you need them.
Apple just plays with apple SO great ... I love the integration and simplicity.