What in your opinion is worse...being a yeller or a spanker?

Kind of a loaded vague question don't you think?
Not every word is harmless and not every spank is damaging. Yet, every parent loses their cool and might yell from time to time and some parents can manage to raise kids without ever giving them even a little swat on the butt.

Being a yeller to me is the worst! You NEVER forget the words that are spoken to you.
I don't like spanking either because my parents were quick to do both.
I still hear their words of anger and I'm in my 50's!

Under the right circumstances, I don't see either of those options as being bad or wrong. There are more damaging ways to parent than yelling and/or spanking.

What's worse is a parents who doesn't discipline their children at all!!!!

I assume "worse" meaning what is worse for a child, what is more damaging. What matters is the child's individual experience, so I believe there's no "authoritative" answer to the question outside of a specific context.

I think it's a good idea to strive to be sensitive to the potential harm of either.

I don't like either of the choices, but I'll admit I've lost my cool and done both occasionally. I guess if I were forced to choose, yelling to me is worse because it implies being out of control, where spanking may be done calmly and deliberately. My parents were both chronic yellers, and their raised voices still haunt me even though I've been out of their home for over twenty years. Belittling, name calling, and harsh scolding can break a child's heart. Spanking done in anger can, too. I still remember my dad pulling me over his lap and spanking me for something when I was in early elementary school, I don't recall what, and then shoving me roughly off his knees so that I landed on his boots crying. That cut deep. I just try to be the most loving parent I can be so that my daughter's experience is different, and I've been known to apologize to her for losing my cool and yelling. It seems the only fair thing to do.

How about just not being crazy?

How about taking parenting classes before having children and learning there are more solutions to the problem than yelling and striking a child (both are abuse)?

I'm neither, and my kids are well behaved. 

Being a yeller is worse. Now that my children are grown, I can see that some of the words I spoke or yelled at them did a lot more damage than the few swats they got on their behinds. The swats were soon forgotten; the words live forever!