We all know that nobody takes down the neutrals like a Valkyrie. But for other middle game considerations, people opt for other heroes to start with, mostly a Barbarian. However after loosing my Barbarian to a Heavy infantry in +5 city AGAIN and watching my partner loosing it to an Eagle on +10 city I finally decided that Barbarian isn't a great starting hero. I would call him a high risk high return starting hero.
1) He is relatively slow (14 moves)
2) He is relatively dumb (90 intelligence)
3) Can't search ruins (low undead lore)
4) Can't help other troops (no stack bonus)
As a high risk high return hero, if you can get him to level 2, it pays off greatly afterwards. But you may loose him on the way or loose most of your starting troops. On average, he has to capture 4 cities to level up as opposed to 3 cities for most other heroes. Even if his chances are 90% each time, this is still a considerable risk. He either goes on front and take the risk or watch the starting troops parish.
Of course it all depends on the map and starting troops. I may still choose him if I can accompany him with a battering ram or maybe with a Yeti early in the game. But in large maps or rich maps, I just gather enough gold and wait for a level 2 hero offer and get my 44 Strength barbarian that way. Call me lazy. Sometimes I accept level 1 Barbarian as a second hero if I have enough stack bonus units.