I've heard a lot of conflicting suggestions in the past regarding dialogue, so I'm hoping I can get a solid answer here.
Some people have told me that the best way to go about dialogue is to make it as compact and to-the-point as possible. Good dialogue, they said, should not sound anything like the way real people talk. Dialogue should reflect the meaning of what's being said—not what's actually said. There's no "um"s or "uh"s; hesitant pauses and stutters should have no place within the conversation. Slang and dialects should not be reflected in writing, so it's
"It's about time we got going, don't you think?"
"It's 'bout time we got goin', don'tcha think?"
I'm not a fan of this approach. I've always liked writing dialogue as if the characters involved were two real people having a real conversation (so, between the two quotes above, I'd take the latter over the former). Additionally, "um"s and "uh"s can say a lot about a character, the way I see it, and if that character's characterization is important to the story, I'd want to put those "um"s and "uh"s to good use.
But now I've come to a point where I'm afraid of being too realistic. What if one of my characters has severe anxiety, and I want to reflect that through their speech (since it's relevant to the plot)? This character would stutter and backtrack through their words a lot. It's a lot tougher to read, but that's the point since this character's speech is hard to understand.
And what about dialect? I feel like dialect can add a lot of personality to a character's voice. If one of my characters is from the deep American south, I would want to write their dialogue so that it reflects the way that character would actually talk. Charles Chestnutt's "Po' Sandy" was almost completely narrated by a character who spoke in a thick dialect, and though it definitely took a long time to read, I felt like it was worth it in the end. The story wouldn't have been the same if it had been written in standard English.
So, when writing dialogue, which approach is best (or generally accepted by most people)? Should it be precise and only aim to capture the meaning of words rather than the words themselves? Or should it be as accurate as possible, even if that means that the speech will be harder to read?
Should I write easier dialogue if I'm writing for a younger audience? (Young adult vs. adult fiction?)