Best National Hero?

[Sheap]

I'm going to have to go with Etimmu the Wraith Lord (undead Ermor, both themes) and Angerboda the Great Hag (Jotunheim, all 3 themes).

Etimmu is a regular Wraith Lord, except he's mounted (not really an advantage in this case since it costs him a slot), and comes with unholy priest abilities. It's like getting a 40 gem, conj-7 summon for free, and Ermor can easily take luck-3, and get him in the first 10 turns or so.

Angerboda is a powerful Jotun Hag with 44 HP, two built in resists and a whopping 11 magic paths, although (except for S3) they mostly duplicate the already available Jotun paths. The S3 can be awkward in case of magic duel, but if you're not fighting Pythium or Arcosnuffle she's just about indestructible as combat mages go. Unfortunately, Jotunheim also normally takes Misfortune.

Burkhard Nachtzehrer is great, and needs only a blood thorn, shield, and boots of quickness to be a real force for destruction, what with his built in flying and resistances. Unfortunately BF Ulm requires misfortune 1, and usually adds another point or two of misfortune on top of that, so he isn't seen very often.

Ambicephalos is good too, for all the reasons you mentioned, and since Pangaea usually takes Luck, heroes arrive relatively often. On the downside, CW Pan has so many heroes, the chances of the hero you get actually being Ambicephalos is not so great until later in the game.