I'm not saying perfect kings english but more so in a way that the character has had proper education and having them talk in a way that makes sense to the viewer. Don't take MZero and combine it with Frasier. Make it sound natural as if the lines were coming from the person versus someone just reading it off a piece of paper. An example of this would be the dub of Cowboy Bebop vs. the dub of DBZ. Cowboy Bebbop sounds more natural where as DBZ sound like a someone just reading their lines at times in my opinon.
If the script calls for the character to slur his/her words then so be, but NO EBONICS.
Making it teen-ify is a stupid move because it wont withstand the test of time ie six months.
An episode of Frontier where they all talk as if they're on Frasier.... that would be hilarious.