Dildo / Vibrator - More Effective With Ribbing or Without Them?

Do dildos or vibrators have different sensations in a vagina wether they are smooth or ribbed ?
Can you actually feel any difference when they are inserted or do they both just feel the same. Or do ribbed / beaded types feel more stimulating than a smooth type?

 

If they are only slightly ribbed like a condom, it's no big deal to me. Give me a significant rib, say the size of a vein in a penis, now THAT is going to feel good!