This.
His disciplinary record is bad, and he gave away many penalties as his judgement is bad - the thing that annoyed me most about him leaving was that he was putting in inept performances and costing us games on a Saturday then in the papers on Monday he was saying how he was leaving as if he'd become to good for us! It showed incredible arrogance.
Neill and Brett Emerton are very similar. They are two good athletes - in great shape and very very fit. However it looks as if someone has spotted them at a young age, noticed their athletic prowess, and tried to turn them in to footballers. As a result, they do not have the natural ability that you would expect of Premiership footballers born and bred in football dominated countries. This in turn results in them making bad decisions and having suspect judgement.
The difference in my view is that Emerton is without the dodgy temperament/attitude that Neill has, thus making him the (slightly) more attractive option.