RecForge II (Android)
This app allows you to record in MP3, M4A, OGG, WMA, OPUS, FLAC and WAV formats. Other useful features include options to skip silences when recording, use an external mic, manual gain adjustment, and more. A pro version is offered for about three dollars.
Voice Record Pro (iOS)
This app allows you to record audio in MP4, MP3, and WAV formats (and will convert files between these supported formats). You can also export/import to various popular cloud services, add effects to recordings, and more. A version without ads is sold for $6.99.