I voted for Ancient Greece, The Future, and Other Dimensions. I'm with Louise about the absence of antibiotics and adequate plumbing during many periods of history, but I still would love to see the height of Greek civilization since I've been fortunate enough to see it during modern times.
Otherwise, I'm all about the future and other dimensions. I think it would be so exciting (and perhaps dangerous) to see what becomes of civilization and humankind in the next 100, 500, 1000, or more years.
Other dimensions? It boggles my mind, but if we had the technology to do it, I'd go for it! Maybe I could be an explorer and they'd name a street or town after me!