I delayed the MMR and prevnar for DS2 simply because DS1 has ASD. But I knew that DS1 had ASD (well, I knew something was different) from his earliest days, so I knew it wasn't that.
I was vaccinated against measles as a child, and have no immunity at all now (had to have a blood test while pg as exposed, but luckily didn't get it.) I had mumps twice and rubella aged 8 weeks, so am nice and immune to them.
I think, if you could guarantee that the "wild" version would be complication free, and that the child would be fine in a week, then it is best to have that. But you can't, so vaccination (IMO, for my children) is a better choice.
I have worked with kids who had ASD caused by encephalitis, caused by measles, and one child who had Congenital Rubella Syndrome, which is very disabling indeed. Definitely influenced my decisions.
Oh, and the chicken pox thing - I am worried about the shingles effect that is being experienced in the US, but I am aware that CP is not always a mild illness - both DD and DS1 ended up on antibiotics, DD due to infected scalp spots and DS1 due to infected spots in his ear canals, which was horrible. One of DD's friends had septicaemia from CP and spent 2 weeks in hospital. So I think, if there is more research about the shingles connection, and it is offered here, we will consider it for DS2.