I'd use SimplyDrop - I just sold the same phone as yours (last week got £293, price now £245), posted phone on Monday, delivered to them 11:15 Tuesday, email from them 12:30 Tuesday confirming BACS credit processed and money in my account by Thursday - I'd never use anyone else, 3rd phone I've sold to them and similar good experience every time.
Not heard of SimplyDrop before but will keep them in mind going forward, thanks