Which type of wood flooring is more dog friendly?

We have two 50 pound dogs, one of whom has inflammatory bowel disease. So we need to take into consideration scratches from doggy toenails (which is really not too big of an issue, becasue we keep them trimmed pretty short), as well as cleaning up frequent messes. What do you think would hold up better? Laminant? Engineered hardwood? Real wood?