Definitely Janet Evans.
I remember watching her WR 400 at the Olympics on TV and just being amazed...
(and thinking, wow, I could start at the same time as her, sprint my brains out for the first length, and she would still flip before me... then go on to do 7 more lengths!!!)
:D
My favorite swimmer was Mark Spitz too.
I recall that his record setting victory restored some jubilation to the 1972 Olympics in spite of that depressing terrorist attack on the Israeli athletes.
Happy Swimming
Dolphin 2 :D