Hell or Hell was by far the hardest mode, however if you go back and beat DMD, you unlock Super Dante, which has infinite DT, which basically turns HoH into a cake walk, the hardest part then being the last boss, which just comes down to memorizing his patterns and playing it safe.
Also, to get a Triple S on all the Nephelim missions easily, just use the Demon Evade and Trinity Smash combo, it's a triple S in style every time and your points will go up hella fast. Also, DMD is fairly challenging and more if a sludge fest, however just but a bunch of yellow orbs for the last fight, and at least one large Devil Star.
Also, I'm kind of bummed there wasn't a rare artwork for getting all the achievements, does anyone know the requirements to unlock them? So far the only one I got was play for 50 hours.