I use neutron music player app on my iPhone.
Plays everything and you have ftp support too, so that you can copy tracks over to your device and not have to rely on iTunes.
It plays flac and everything else you can throw at it, and also gapless playback for MP3 works on both lame encoded albums as well as albums/mixes that have been encoded with iTunes and contain the iTunes gapless tag metadata.
The stock iOS music player has bugs in it which causes random gaps/pauses between some transitions on albums. And also lame encoded MP3 albums don't play 100% perfectly smooth gapless playback, it's not very noticeable but it's there. Neutron fixes both of these issues and play all my MP3 mixes fine.
Cue sheets are a gift, I make my own and can split up long mixes into separate tracks and have them all tagged, named and numbered.