start with the ninth doctor Christopher Eccleston mostly because you get ot see a lot of the fabulous Billie Piper as Rose, his super hot blonde companion.
Then go on to the 10th doctor and my favorite so far David Tennant who played the character from the end of Eccleston's doctor in '05 to the current one. Tennant had some Billie Piper as well, but then had some annoying companions with the exception of Martha Jones who is also a looker.
Then we get to the current doctor who I don't really like that much yet, but is growing on me. However, the only reason to watch this latest series is for the hottest companion in the history of Doctor Who, Amy Pond, played by Karen Gillan. And the last season was shot in the USA with some fun scenes in Dick Nixon's oval office.
and it goes very well with punkin ale.