I'm torn between a few candidates.
Argonians - They just seem lame by and large. I'm cool with Khajiit since they have funny voice but Argonians don't have even that. They just come off so sub-human to me that... I don't dislike them, it's even worse - I don't care about them. I find them wholly uninteresting.
Bosmer - Closest thing TES has to stock elves, which is enough reason to dislike them. Tree hugging, bow-wielding elves are way overdone in fantasy. Dark and High Elves are nice change from that - while both are tropes present in most fantasy, in TES they are done differently from their usual adaptations that they come off as sufficiently different. Bosmer just feel half-assed compared to their more prestigious cousins.
Nord - I despise Vikings, I despise Hollywood Vikings. I despise the fact that when (usually American) companies want to incorporate something from pre-Christian Europe, they always go for the damn vikings. And with so little change! Before Skyrim the Nords were as stereotypically boring as they could get and in Skyrim it's only their sweet ass backstory that makes them interesting. Beards, axes and ale, that trio is so way overdone. It makes me throw chairs when I see Hollywood vikings. When I started recently playing Mount & Blade, I immediately decided that I would not stop until every Nord (yes they are called Nords in that game too) city is a ruin.
Of these... Hard choice. Argonians are so dull that I won't even bother voting for them, Bosmer too, and Nords at least have some redeeming qualities in their backstory. Heck, I'll go with the Nord. I wish the Vikings would just vanish from history and no one would ever discuss them again.