Soldato
I only tend to shield against mobs thats have long range attacks, everything else i two hand but always stay light enough to roll fast to get the hell out of there if i need to. As for O&S, i always summon Solaire, he keeps fatty occupied while i smash skinny, its just a question of how fast you kill him so Solaire has a decent amount of health left to join you in taking on super fatty.
Then I think my only option now (now that I can down the large giants with ease) is to farm humanity and tackle it with him.
I've helped a few people out by being summoned, but none have won, I've tried solo a fair few times and the jist of it is easy enough. It's just I get caught out, pot up, caught out, pot up... Then by the time I down the skinny one, I'm out of pots pretty much and the fatty just dominates me.
So yea, I will get some humanity and summon solaire