I went with felhunter for my nelf DH. Dude's full of shit when he says shivarra and succubus are the corresponding choices to each spec; it doesn't matter what you choose and a felguard's as good as anything else.

I went with gan'arg for my belf due to her being an engineer, and well, it made sense. I know someone who had their DH consume an imp, and another who's got a felhound. TBH the only ones I would stay away from are nathrezim or eredar.