I'm also tempted by a Durge paladin run, attempting to resist the urges. Like the OP I think there's real potential there for roleplaying the struggle between principles and something dark in one's nature. (And while everything's speculation at the moment, I don't think Durge is intended for solo runs specifically - obviously if we end up killing all our potential companions then we're going to end up alone, but I am expecting that we have considerable flexibility in how a Durge run shapes up just as we will for any other origin, though possibly less than Tav.) I'm definitely not going Durge for my first run though.
When it comes to lawful good, I agree with ladydub that the best bets outside of paladin are probably a good cleric, a fighter or some kinds of wizard. Though while I also see rangers as more neutral to chaotic, I do think they could be roleplayed as lawful good if we focused on, say, a Hunter serving a temple or some more temporal power. Warlocks I also struggle to see as lawful good, as it feels as though making a bargain for power with some being of questionable morality is in tension with that. But we could possibly come up with a story that makes it work, for that or practically any class. After all, the only person we need to convince in single player is ourself
