You've left out gacholoths, which are possibly my favorite kind of yugoloth. (They first appeared in a Dungeon adventure, and later in one of the MC Annuals.)
Oh...also, marraenoloths. Ooh, and dergholoths. Can't forget them. And yagnoloths, of course. (And possibly others; I'm just going from memory here and there may be some more I'm forgetting.)
Well, in that case, you can't forget hordlings and diakka, the two most common creatures on the Gray Wastes. (Neither of them is really necessarily an "exemplar", but they have at least as good a claim to the title as night hags do.)
What, you're including Carceri and Gehenna? Well, if you're including Carceri, you certainly have to include the gehreleths. And...well, actually there are a whole lot of other creatures also inhabiting Carceri, the Gray Waste, and Gehenna (phiuls and vaporighu, to name just a few more); your best bet is to look in the encounter tables in the Planescape Monstrous Compendium II for a more complete (though still not exhaustive) list...
But I'd limit the poll to something a little less broad. Like I said, there are a whole lot of different types of creatures inhabiting those planes; maybe you should stick with just one of the planes for the poll, or even just with actual yugoloths.
I am going to run a poll to see which loth type is in the greatest need and most deserving to have more stuff written about them.