Good, no contest. I wish there were more games that made Good the more challenging path. I play Good because I want to be the hero. To me, being the Hero means to protect my comrades and the innocent, to overthrow tyrants or slavers, or to encourage growth and prosperity if the country's politics are suited to health and goodwill of their fellow countrymen.
Evil 'heroes' protect their comrades as well, but they abuse the innocent. They typically overthrow tyrants so that they can become the next one. They encourage growth and prosperity only if it profits themselves the most.
I'm ok with playing Evil, but abusing the innocent is really hard for me. Hell, some games have you sadistically torture innocents, and that's usually where I draw the line. (Let me point out a difference between instant gratification GTA killing sprees and drawn out plots of torture. Chaos can be fun every now and then, planned torture isn't to me. Really, every time I go an a rampage in GTA is just to get the attention of the police. I perfer targets that fight back.)
But all and all, they are both usually healthy expressions if kept in context. I think Steven King said that the human mind has sewer gators that need to be fed occasionally.