Even the Fortress of Raze is not so easy to begin with (I'm now level 27) ... but big fun !
Me too love the human form a little more just because the battles in dragon form are super big fun BUT to fast over/done in comparison with the human battles and gathering loot form crates, barrels and chests ... searching everywhere I can takes time ...
When I start a Flying Fortress I first fly around to get an "overview" and then start in human form, mostly all the way down first (like Raze said : at the bottom and way up to the top

)
If I wish to fast(er) make big XP I blow up some Ballista's or ...