I'm in the same boat as Selindrile. If I want to do something, all I need to do is ask my LS. We may already have plans for that night so I sometimes need to wait a day or so, but it gets done. I join pickups sometimes just for fun and to meet new people, but mostly I roll with the linkshell.

As for favorite Ambuscade set-ups, my favorite is with a war.... tomahawk makes this fight easy mode. We usually also use a GEO, no matter what the setup. Other than the WAR, WHM, and GEO, the other 3 slots get filled with anything.
Some other setups involve THF and DRG of course, but you forgot BLU ! Blu can deal all 3 additional damage types rather easily. Our runs last night were BLU, DNC, PLD, WHM, GEO, and SMN. We weren't setting any records but the mob only lived long enough to pop 2 groups of adds. Not as fast as having a war, but we were still killing in under 4 minutes.