My LS uses Light Skillchain on everything. You should see the awesome Firaga3 MBs on Suzaku, and those massive Thundaga3 MBs on Byakko. It is quite literally... awesome. It does take us a little while to kill Aspidochelone, though. For some reason, man, he just Regens it all back all the time. Turtles are weak to Thunder, right? Maybe our BLMs are just gimp.
Also, we only use Light and Thunder on Fafnir, even though we heard this weird rumor that other LSes use Water MBs also. I'm not sure I've ever even seen a Darkness Skillchain, but if I were to want to start one, I would obviously throw the PLDs, NINs, MNKs, and THFs in there to deal out their obviously superior to DRG damage as they swung constantly and either hit for 0 or missed their asses off. But, since everything is weak to Thunder, we only use Light Skillchains.