I can't say that spanking makes a person better or worse. A person will decide if they are better or worse - parenting has influence and so too does society, of course, but it's all down to the individual. Take it from me: someone who got spanked.
Actually, I wasn't simply spanked, sometimes I got the stuffing beat out of me with a thick leather belt and buckle for something as simple as getting a B+ or lower on a test or homework assignment. My mom was quite brutal in that respect. My dad refused to take part in the beatings, but couldn't do anything about it, considering my mom is that extremely dominant type, while my dad is an engineer who believes in shutting up, doing your job and minimizing conflict. In any case, all that left distinct (albeit cleverly concealed) bruises that would certainly have gotten Social Services called if I dared reveal what was happening. Mostly, I was too damn scared to say a thing about it. Yeah, Asian parents, if you didn't already guess.
Certainly, it fostered a resentment towards my mother. Though we get along much better now that I'm in college and a bit over a year from graduating and getting commissioned as an Army officer, our interactions haven't quite been the same. Ask me my most distinct memories from childhood about my mother and all I ever think about are beatings for not being perfect in school. No, home wasn't a happy place for much of my childhood, and all that beating never really did change the fact that I was a well behaved kid who was smart, but impatient with bullshit academic subjects and wanting to apply himself to worthwhile things. So I graduated high school with a substandard B+ average. And I'm nothing amazing in college either. Much better than many, but certainly not to Asian parent standards.
However, I think I turned out just fine. I'm an Army officer cadet - I'm physically fit, trained in warrior tasks and drills and I am in command of a whole platoon of younger cadets. Not that this is anywhere equivalent to actual soldiers, but I'm learning and will become a commissioned officer in less than two year's time. I have a sense of moral discipline, pay for my own schooling via scholarships and have a vision for my future. A lot of people who claim to have had happy, carefree childhoods cannot say the same right now.
So does spanking make a better or worse person? Hard to say. All the "spanking" did for me was reaffirm my own independence and realization that, as a citizen of the United States, I did NOT have to conform to my mother's traditional ways. She chose to immigrate here, she chose the US as my birthplace, and this being the land of opportunity, I'll forge my own path, whether you like it or not. Break my ass with a belt, but you don't break my strength of will.
Long story done.
EDIT, AFTERTHOUGHT: I will never condone overtly harsh spanking as a punishment on a child. Sure, sometimes you gotta just whip out Ol' Faithful and paddle them upside heaven till they learn (do NOT misinterpret that you perverted scag, you know what I mean). But I've seen what people with lesser strength of will have devolved into with comparatively easier punishments. Even a harmless slap is still terrifying to a child. Sometimes, you have no choice, but point being: never make it lightly.