Start with Manual (mean direct link between radio and servos) and fly, adjust the roll differential if needed.
Next fly using Rate with default stabilization settings, basically if not responsive increase P, if servos oscillate: decrease P.
You should use TxPID do do that and test Roll/Pitch Proportional term in flight:
https://librepilot.atlassian.net/wiki/display/LPDOC/TxPIDAnother good stabilization mode is Acro+, this mean Rate around middle stick and Manual at full stick.