For Tanking:
I've fought Arch Omega and Arch Ultima that are of note so far, and I D/C'd half way through Omega so couldn't get a brilliant idea of hate/resist/damage mitigation etc. however, I think that /NIN is definately the way to go. Sure the PLDs had hate for the most of the fight, but Omega has colossal blow and pile pitch which reset hate, and Ultima has Citadel Siege which is insta-death (never tried to use CS on me, so not sure if Pflug would help).
I only did them once each so far as well, and I was trying to get a feel for damage output as well as party buffing, dodging attacks etc. so I wasn't full-timing flash and/or foil, which (certainly post foil enmity update) will be required if you want to tank.
What I found: it seemed fairly easy to keep shadows up, even despite the fact that I'm our group's Empy bard, so we had no march and no elegy. Though on Ultima, after the 2nd of the 2 PLDs died and I started tanking full-time, he did seem to have 100% accuracy on me even in eva gear and swordplay, so maybe I just got lucky that by the time I lost 9 shadows he went into countdown.
Speaking of countdown: This was used 3 times during the fight. The first one, the WHM Sacrosanctity'd and we all took almost 0 damage. 2nd one, I used One For All (recently got Dissipationed so I didn't have 3 runes up) And we all seemed to take ~500 damage. 3rd one I used Valliance with 3 dark runes and again we all seemed to take ~500 damage. I was just eyeballing the damage, mind and had filters on for that fight so I would assume that I actually took less damage than the others, but I'm Taru so maybe we all ended with a similar HP, rather than took similar damage. After all, I had +96 light resist.
For the Omega fight, before I had been D/Cd, I didn't have filters on and I could see that AOE damage TP moves were doing double digit damage to me, but ~250-300 to the 2 Ochain PLDs. I can't remember which TP moves they were, or whether they were breath-like as I was stood slightly off to the side, so that might have affacted it. From what I remember, I was using barblizzard, barparalyze and 3 x wind runes on Omega, to avoid paralysis.
Ok, on to DDing: I've only tried /SAM for DDing and it seems fine for when you're in a situation where you're not going to need to re-appy buffs while being attacked, or need to ride recast timers. I also use this for soloing EP mobs for weapon trials, riding hasso and phalanx. As long as you re-cast phalanx before it wears off (and maybe use -PDT gear while casting to ensure you get hit for 0) then this isn't an issue.
If you are really definately never going to get hit, or are in VW full-timing fanatics, then /WAR has got to be better, but RUN being so squishy, you need some form of damage mitigation against anything worth-while that might face you, or has physical AOEs.
Soloing: As I said, SAM for EP mobs, but against T mobs I'm still unsure. I tried /DNC in adoulin, and that sucked. I then tried /SCH and that was better, but still too much casting, and without designated macros for the fast cast stratagem, I was dead before I could get SS or blink up again. /SCH was nice for paralyna though. Other options are /NIN or /RDM or even /WHM, but I've not got around to any of these yet.