I don't think executing Saddam would make him a martyr. A martyr comes when you kill someone with spiritual/religious significance (eg, Yassin), or someone who ruled via cult of personality (eg, Lenin). Nobody misses a thug; there might be people loyal to him still*, but I doubt it's because they love him so much. Which also means, not going to be a martyr if he's in prison either... but from prison, he can still communicate, and has the left-field chance of something happening to get him free (odd, but possible). Don't think Che. Think Noriega. Would anyone say he's been a martyr for a cause?
--Dan
*But we're getting them, one by one.