I have to go with Lynyrd Skynyrd. They definitely defined what it meant to be "Southern Rock". A bit of trivia........did you know Sweet Home Alabama is a reply to Neil Young's "Alabama", which spoke poorly of the southern state. Don't get me wrong, I really love ZZ Top as well. Billy Gibbons is one of my favorite guitarists. What most people don't realize is how "mechanical" a lot of ZZ Top's music was. Frank Beard is definitely a very capable drummer, but for some odd reason a lot of his parts are done by a drum machine.