I would add that warrior, to me, doesn't seem like a great class for exploring.

If you're willing to be good-aligned, then some flavor of paladin or a orderly conjurer seems better.

If evil, then maybe a hero necromancer, predicated on being able to raise a large army and make use of haste staves, but I'm not speaking from experience here; just speculating. Liberal use of haste staves would require that you to know how to raise lots of coin.

Bard and assassin are decent choices that work for all alignments. Assassin having the advantage of detect hidden, bind wounds, vanish, and trance. Sometimes blindness dust is useful too.

Ranger and thief have niche applications for exploring *specific* areas. Thief, in particular, has an easy time mapping out a couple "dangerous" areas by way of gentle walk. Peek and steal also come in handy. But you're pretty sub-standard when it comes to killing mobs.