I am having a heck of a time deciding between Custom and Durge for my first, and probably only, playthrough. I have played the other two games many times, so I understand how the Durge relates to them.
Which would you choose for your only playthrough and why?
I would still suggest playing as Tav before playing as Durge. Can you run before you can walk? You can try, but it'll probably be more enjoyable if you have a base understanding of the game. I actually loved my second playthrough as Durge more, because I knew what to do, and where to go.
Here is my reasoning:
1. You're unfamiliar with the map, don't know where to go, don't know where the battles are. This means there's a higher chance you'll land yourself in surprise ambush attacks/difficult battles you didn't have to fight.
2. You're learning the controls and the mechanics
3. You have to learn the classes and figure out how you want to spec the characters and their skills
4. You're learning the overarching storyline, and learning the other character's backstories.
5. If you're trying to trigger certain scenes, sometimes the Durge's story will take precedent over companion cutscenes.
So for example, as Tav I got the Astarion bite cutscene very early in the game, probably 2-3 long rests. As Dark Urge, I think I long-rested 7 times, found his exsanguinated boar, finished the goblin camp and was literally down in the underdark before Astarion was like "HEY... I have something to confess, as it hasn't come up naturally... I'm a vampire. Ha."
I think if I had done Durge in my first playthrough, it would have felt a bit overwhelming. I would be annoyed that the cutscenes I wanted weren't appearing. I would also be frustrated that I'd have to kill characters I want to spare. If it's your first blind playthrough, there's no way you'd know how to save those characters unless you read a guide.
I appreciated the Durge so much more, because I had Tav as a comparison. With Tav, being a good character was a given. With Durge, I had to struggle to be good and I felt like I actually earned it.
I say, try Tav and if you love the game as Tav, you will love it EVEN MORE as Durge. Save Durge for your second playthrough, it's absolutely worth it. I swear the second time around there were still so many different things to be seen.