My cavedweller dragonslayer mapped out the Underdaark and found most of the dragons

Any sword warrior with whip or h2h for utility value. I would pick a defense legacy with whispers

Most rangers are very good explorers and can root out a great deal of explorer areas like whistlewood and organia- they will also spot camoflaged mobs

Bards are epic, they can take a group to hell or stand alone. Built in lore, healing, sleeping, calming and area affects.

Thieves can see hidden mobs, steal, pick locks, advanced locks, peek, gentlewalk, combat steal and have epic utility to make up for lack of warrior or ranger power. Thief explorers are on league of their own.

My water shapeshifters mapped out the underwater Thera, which has more than most know

Shapeshifters in general are unmatched in regen and the combination of offense/defense/mobility . Some can camoflage or do other useful things.

Shaman can take most of the game solo.

Paladin can take most of the game solo.

Make a list of the areas you intend to explore and pick your character based on the list.