That really depends on who and what you are serving

If you are going with standing rib roast, yorkshire pudding, creamed spinach or onions, then maybe the latter.

If going with turkey, stuffing, mashed potatoes and cranberry sauce, generally more cranberry sauce is left.

Ham dinner? With sweet potatoes, rolls. And green beam casserole ... probably sweet potatoes.

Then again, some people serve very different menus, everything from blood pudding and headcheese, to lutefisk, pickled herring, goat, elk/venison and okra. I have never come across a universally despised side dish that is traditionally served at Christmas.

My personal and apparently most people's major dislike? Boiled Rutabagas! Easily the most common leftover after Turkey Day! Most guests put a teaspoon to a tablespoon on their plate, to be polite, then leave it until last. They mush bits of everything else into it, then swallow as little as possible, stone cold! I've never found a creative recipe to make them into something tasty, that appear enticing, and make guests want to try them. I serve parsnips instead. The 2nd biggest leftover? Candied yams, buried in melted marshmallow. Ugh! There are so many better savory ways to prepare them! Butter, a touch of brown sugar or molasses, 2walnuts, cinnamon, and nutmeg or apple pie spice, create a tasty side that compliments the naturally sweet flavor of sweet potatoes. They look enticing, people try them and love them. I make a Yam and Apple Casserole that everyone loves, yet it has just a touch of sugar and spice. 3rd Green Bean Casserole!.

Who really wants to eat beans smothered in canned mushroom soup and covered with crumbled stale French fried onions? Yuck! But freshly steamed with butter and Summer Savory? No leftovers! Stir fried with Toasted Sesame Seed oil, Chinese 5 Spices and sliced or slivered almonds? Also, no left overs. Or a side dish of Homemade Baked Beans. Again, no leftovers! 4th, Jellied, canned cranberry sauce, the condiment everyone seems to despise, has it's uses, it makes a fabulous glaze for chicken, Turkey, and pork, for example. But a cooked whole berry sauce or raw Cranberry Orange Relish, are excellent. I've never been left holding a ton of leftovers with either, yet the leftovers are easy to use. Try cranberry-orange relish with fish, delightful.

Us Brits have meat, potatoes, vegetables & gravy, a complete meal. Now which veg is the most unpopular? Well that just has to be brussels sprouts, most people only ever serve them at Christmas. Just why? To add insult to injury some people serve mashed potatoes with Christmas dinner. Just no, I can eat sausage, mash & beans any day of the week.

I will also never eat turkey at Christmas and never really have. You can stick 'tradition', there is just much better meat out there. The days when turkey was a luxury and 'special' are long gone, nowadays turkey is one of the cheapest meats out there.

I think it depends on the people, but in my experience, it's usually brussels sprouts. I think it's because they're so polarizing it seems - people either love them or hate them - so the people who do take them take quite a few, but many won't take any, whereas with the other sides, everyone will take a smaller amount of which seems to end up being a larger quantity overall than the brussels sprouts.