Both run very full in my experience.
The MH operated flight feeds all of KLM's traffic to Oceania from KUL, and has been completely full every time I have flown it.
KL807 isn't marketed by MH for its specials to Australia, but is nonetheless hard to get on because it goes on to MNL, which tends to do well, and is IIRC a 744 Combi.
If flying in economy, I would prefer the KL flight as an elite (for a quiet flight in the select seating area), and the MH flight as a non-elite (KL status does nothing on MH, but the seats and food are superior), making sure to not be seated in the center 5 seat section.
MH's much-vaunted service isn't at its best in eco on this route, which always seems to get a mostly-male, not-too-polished, if hardworking crew. I also prefer KLM's later departure.
In business, I would opt for KLM, due to seat pitch and layout (2-2 @60" on KL's 744, 2-3-2 @50" on MH's 772). This will change next year with MH's new seats, though.