Going negative on another school (assuming it is true information) seems more mature and less negative than going negative on a kid (even if the kid jerked you around).
Depends on how it's done; and I respectfully disagree with what you're alluding to. Miles' comment on Kiel last year was hardly as slanderous as some made it out to be. Context means everything. There's a world of difference between: a) making a kid the focus, saying he has no chest and trying to shine the spotlight on him negatively, and b)saying something to the effect that maybe this kid didn't have the chest to come here, but we still have a great group of guys who have outstanding qualities and they're going to do great things. The latter, which I think was Miles' tack, is a way to say it's time to take the spotlight off of Kiel and move on. It turned out to be not the most politically astute way to say it... and allowed the media to frame more emphasis on him slandering Kiel than he intended, but whatever.
Les likes to smack talk a little; he's not quite as witty as Spurrier, but I'm fine with it. People who get worked up about it are either too sensitive or have an agenda to cut him down.
Negative recruiting, in comparison, by saying another school sucks in some way or another, or trying to plant seeds that coaches won't be there when nobody knows anything, is a different beast. And it is petty and insecure in comparison to a school that recruits by simply highlighting what it has to offer. I'm not trying to be holier than thou, and personally can't say I wouldn't resort to negative recruiting myself if I were a coach, but I do think it's nice Miles and his staff can succeed by doing it more honorably.