My feeling is that the Raiders are least likely to move to LA.
I'm not sure why I care, but I would be disappointed if the Chargers left San Diego. That would almost be like the Seahawks moving to LA. I know the Chargers owner and the city of San Diego have been at significant odds regarding replacing Qualcomm Stadium, but shoot, I'd like to see their relocation bid be denied and all involved parties work out their differences so they're no longer seeking to relocate. Doesn't look promising, however.
Looks like the Rams are in the lead in the race to L.A. Go, go, go!
Addendum:
From a marketing standpoint, Raiders would make the most sense in LA. The "Los Angeles Raiders" just sounds right and fans would love rooting for them. The Rams obviously come second in this regard. But if the Chargers name stays in a move to LA., it would be strange and awkward to root for the "Los Angeles Chargers." Awkward in much the same way the "Seattle Browns" would be if that team moved here and the nickname had to stay.