I try to let a character's characterization determine dialogue most of all, I suppose. Setting and background can have an effect, but on the whole, someone may just have a personality prone to shorter sentences and simpler words even if they are from a fancier background, or someone may be prone to tl;dr like me, despite my plebeian upbringing. XD; Tone and intricacy also are more influenced for me by the character's emotional state and intelligence. I guess I would say I write men differently from women (and occasionally use that silly "What gender are you?" writing tester online to see if I get male when writing in a masculine voice and female when writing in a feminine voice; makes me giggle if I do, though I don't put much credit in it.) I avoid accents whenever possible just because they jar me as a reader. And I have had character voices evolve as I've been writing, to the point that once I'm well into the story, I look back at my first writings and go "Who was that?"