I've farmed mine during Noble Intentions (it is hard to find group which plan to do Final Assault and it probably takes much longer).
I was using heros/henchies team:
Koss - Crippling Slash,
Margrid - Broad Head Arrow,
Olias - Virluence MM,
Lina,
Mhelno,
Cynn,
Eve,
i was Mo/N with Spoil Victor and while i was killing him i have been set up as 55HP build - dunno if he can be solo with ele build .
It was a bit time consuming cause he doesn't spawn always (but in this case you can always go and look for Galigord's stuff). Also you need a bit timing with sending away your heros/henchies to prevent them from killing Rago (with minions it is sometimes problem). But with some luck and patience you should end just as i - with both Galigord's and Rago's set - it was much faster to get them all than to grind lvl 1 friend of Kurzik title .
Just do the FA farm like Yarrick suggested, it is the quickest one for Rago who will always spawn on it.
I'm not too good at math but:
during FA 5-player you have:
100% chance for Rago to spawn * chance for green to drop * 1/5 (assume that other player won't share his loot with you) = chance for green to drop/5
during Noble intentions with henchies you have:
(1/5 + (4/5 * 1/4) ) * chance of green drop * 100% = chance of green to drop * 2/5 = chance to get it during FA * 2
during FA hero/henchies farm you have:
100% chance for Rago to spawn * chance for green to drop = chance for green to drop (highest one but you need to do this quest with henchies)
And for sure it takes less time to complete Noble Intentions than FA.