Short Answer:

/DNC is more of a situational, soloing subjob. It's fantastic for moving down loads of weak mobs while doing trials, farming drops, etc.

At level 90, /45NIN grants two significant boosts to THF: Dual Wield III and Subtle Blow III. This subjob will increase a THF's damage on all mobs and enhance THF's survivability when pitted against hard-hitting mobs and NMs. /NIN is my default subjob on THF.

I have /WAR leveled, but I can't say I use it. I'm no FFXI mathologist, but I'd think that it's somewhat comparable to /NIN. Berserk is a such an incredibly welcome JA on a job as attack-stared as THF. I lowman often enough in Abyssea that I need the shadows and added Subtle Blow from /NIN. I think it would be fun to sneak into an exp alluance on THF/WAR just to play with it for awhile, though.

EDIT: I totally forgot to mention /SAM and /DRK, but I see that Krabnuckle nailed it already!