Again, your build depends on a) how much time you are willing to spend building your explore character and b) what you want to explore.
If you have time and patience, an invoker can potentially deal with anything.
If you don't have the patience for that, then you need to fit your character build for whatever you want to explore. Want to learn a wilderness area? build a ranger. Are you interested in exploring the Coral Palace? Consider a water major shapeshifter. Alignment and cabal associations will impact your exploration options as well.
The first thing you need to do in my opinion is specify what precisely you want to accomplish: my last hero, I wanted to learn the Underdark, so I created my first ranger, a cavern/hunter felar. I couldn't pk outside of the caverns worth a damn (losing entangle and lightning bites), but being able to tank everything in the Underdark made learning the layout of the place far less perilous.