Huh, I'd say the opposite. Joffrey is basically a caricature, one of the few characters in the series who has basically zero redeeming values. He doesn't develop at all, he's nasty at the beginning and the only change is that be becomes more openly nasty after he becomes king. On the other hand, Samwell's more unique and he actually develops over the course of the series.
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I made a living on time trial blowing myself off to cross the finish line at ludicrous speed. -transience