In spanking or not, anything that is hard and solid is going to hurt much worse than something that is supple and has some 'give' to it. (Of course, as you can see in my profile pic, his hand has a nice effect too.
)
Now, RG has used a switch on me - thin, whippy, lots of 'give' - and I swear, it was excruciating. But I still contend that the worst spanking I ever got was with a school paddle (by RG, not growing up). It's simply more solid and its impact is greater.
A switch was never used on me growing up, however.