.MKV is extremely important! The only format with Multi-track and wont get corrupted if xsplit crash
MP4 is great due to multi-track, but XSplit crashes often enough that important footage often gets corrupted.
FLV does not get corrupted if XSplit crashes but does not support multi track.
MKV has multitrack audio and does not get corrupted during crashes. I do believe this is one of the most important features to add to XSplit soon!