Busch Gardens is quite a circular park by nature; once you've started going in one direction, you can't cut across the park (unless you want to backtrack all the way) so you're probably better off continuing round the circle. Therefore the only real decision is whether you start off going clockwise or counter-clockwise. Clockwise you'll hit Iron Gwazi first, then Sheikra, Tigris and the water rides. Counter-clockwise starts with Cheetah Hunt, a small detour to do the rides in Egypt (Montu, Cobra's Curse) before heading up to the Serengeti area. Both paths will meet up around Kumba and then you'll follow the route back round the other way.