[Aerich]

Another reason to take orcs (at least for a first racial enemy) is that by the time you get to yuan-ti, a ranger (unless mc'd to an arcane caster) generally has a good enough BAB. The +5 essentially doubles the ranger's BAB against orcs in the early game. If you take enough ranger levels, yuan-ti would be a decent. Orcs and gobs aren't bad for HoF choices because the party will be at a lower level than later on, thus perhaps gaining more benefit (proportionally) than against a racial enemy that shows up later in the game.

I often take trolls in IWD2.

I wouldn't agonize over the racial enemy as it pertains to HoF mode. Chances are you'll depend more on summons, enchantments, evocation bombardments, and instant-kill spells than warrior abilities.