The problem is when these characters get too powerful. You can have a series about the Devil himself and make it good (see Lucifer), but you need to scale his powers down. Seeing life from Darkseid's POV would be great, but it could work mostly as a mini or maxi series. Whereas a human character, no matter how powerful, still is pretty weak compared to such godly entities, and thus, works.
Generally, while I alternate between Iron Man and Doom, I also alternate between takes! For Doom especially, I had an idea that would be a big deviation, but it'd make for an interesting take. See, I've been high on Star Wars these last few days, and I started toying with the idea of a SW-themed Marvel story. We'd start with Doom like in my previous pitch, but after his 20s or so, he'd be taken in by Magneto, who after WW2 stayed in the shadows and became a force of good. Due to his slow aging, he'd be a white haired Fassbender instead of Ian McKellen. Anyway, he'd be the Obi-Wan of the story, being both a mentor and a friend to Victor. Wanda would be the Padme of the story, and Pietro I haven't worked in yet. Either way, for a long while, we'd follow Doom as a legit hero, maybe this Universe's Iron Man. That'd make his descendt towards the dark all that much more detailed I think.
Either way, at some point his feelings of frustration would cause him to turn to the occult and seek out the Ancient One. Considering him an idealistic fool as well, he'd turn to the Marquis of Death (the Emperor). Eventually he'd turn into Proto-Doom, with the hood and everything. Things would play out like in EP.III, with him going against Magnus and killing Wanda. Magnus saves his grandkids (Kristoff as in Kristoff Vernard, Doom's adoptive son from 616, William as in Wiccan, and maybe Valeria). And then we move on to a full-on Doctor Doom, with Wiccan as Luke, Valeria as Leia and Kristoff as a mix between Kylo Ren and Cade Skywalker. It's not something I'd ever write because it's essentially a copy of SW and borrows a lot of characters from other properties, but it'd certainly be a nice experiment.
It's mainly this why I don't know which character to choose, really. If I go with Doom, there's more to be told about him, but due to the nature of his character, you run the risk of watering him down too much if you have him as the central character at all times. It's why I'm leaning more towards my original "Iron Man" idea at certain times. See, I had this "pitch", of Tony and Vic being co-stars of such a book. Tony would start as an arrogant prick due to life's circumstances (see the previous IM related posts), and Doom(same, see the previous DD posts) would start out as idealist, but the more they'd see of the real world, the more their POVs would change, resulting a classic Obi-Wan/Anakin rift, but without being a copy of SW. So that way, I can both write Victor consistently and explore his side of the world, and not write him enough to water him down and "lose" the Doctor Doom persona.
The Stark segments would deal with the modern world, and the Doom ones would deal mostly with the old one. Stark's would be about undyinghuman ambition, and Doom's about the utter insignificance in front of the cosmos. Stark would grow more hopeful and would start letting go of his problems and start being a better man(though not to the "cookie-cutter" extremes, like I said, he'd still be a womanizing prick with a God complex, he'd just be interested in more than than just himself), and Doom would do the exact opposite. I think it'd be interesting to see these two philosophies and "roads" clash. No one is technically wrong, because yes, in the face of Cthulhu, humans are insignificant, but on the other hand, it doesn't make our lives any less real, any less happy, painful or "fake". Also, "Iron Man" as a title would be more of a reference to their respective transformations than just a super-hero name. Tony would become a man encassed in "iron", who'd actually be a man f iron will, and Vic would become a man of iron will, who's actually trapped in his own "iron prison".
PS: I've been watching a couple of WW2 themed movies these past few days, and I've started putting the basics together for an AU Marvel Universe where the Nazis won. I'm thinking of Red Skull discovering mutants early, and seeing them as the next step of human evolution, taking in a young Magneto as his protegee, killing Hitler and moving into a "House of M" style modern day MU. It's still rough, but it'd be interesting I think.