Loads are sometimes a hard thing to nail down as well, but can count for a LOT. I try to avoid flights like ATL-HNL or EWR-HNL or MSP-HNL because they've got the bad combination of long flight times and few or no empty seats (also domestic service standards but counts as international for upgrades, i.e. worst of both worlds). I'd actually rather connect on the west coast, and possibly have the overland segment upgrade eligible (though those are much harder to get now.

If either option has a clear advantage on probability of empty seats, I'd take that. Though in booking in advance it's hard to tell, even if you can see the seatmap. I noticed on a trip to BKK on KE last year that KE seems much more likely than DL to have empties on the long segments, though around Korean holidays I'm sure that dries up.

So buy low and sell high.