What herb goes well in a sweet potato and beet salad with a citrus dressing?

I agree with trying thyme. That came to mind first when I read your question. I'd love to hear what you try and how it works out as this dish sounds delish.

Parsley leaves!

I'd go with parsley if it's not a cooked dish.

tarragon . I love that anise flavor with the beets and citrus.

how about dill? i also find that parsley goes with just about everything.

My best guess is cilantro, or maybe some dill.

I'm 'tasting' thyme, especially if you have lots of onions with it.