I like the southern tier a lot (atleast parts of it). Enough to go on the full tour, I dont know. But Ive heard/read about the different advantages in going East-West and West-East.
If it were me I would probably start out in Florida and go West. Starting in the East would give you more time to ride into better shape before you hit the harder grades in the west. Also I think the scenary in the west would be a better prize as you finish the tour.
But Ive heard that when riding the southern tier East to West you will face more tail winds.