In my experience SAM/DNC is very good for things like campaign, and EP-T mobs that don't have a "bad" TP move.
In campaign, if you keep track of the hasso/seigan timers you can pretty much never die*, but, it takes some concentration. Use Hasso for WS, use Seigan/Third Eye so you can throw some Cure Waltzes on yourself, then Drain Samba II and Steps are all it takes to maintain your health during the battle.
For things like FoV mobs (ex. Cape Terrigan), SAM/DNC is also very good, especially for EP-T mobs. Where it DOESN'T do so well is on mobs like Manticores, where some of those TP moves will have you spending all of your TP on healing and not on WS's.
*Except for BLM-type mobs, then you will die--alot.
Basically it comes down to your playstyle and how well you do with whatever subjob you choose. I personally dislike /nin, but that doesn't mean it isn't good, and you WILL find that /nin will do miles better than any other subjob for certain situations.