I believe shallots have the highest carbs (by quite a bit) of the onion family, I found this online just now
All values shown are for a half cup.
Green Onions / Scallions
It is the green “leaves” of this onion that are eaten. The bright green tops are used as decoration in soups, salads and vegetable dishes.
Total Carbs - 4g
Fiber - 1g
Net Carbs - 3g
Italian Red Onion
These colorful onions are often used in salads to add a lively color to them - either a ring or two laid on top, or diced red cubes are tossed over the top of the salad. Italian Reds can be sweet like a Vidalia or more mild. These are usually served raw in salads.
Total Carbs - 5g
Fiber - 1g
Net Carbs - 4g
Pearl Onion
Pearl onions are small, white onions that are often used in beef stews and other meat dishes. They have a mild flavor and are usually served whole, cooked in the sauce or juice of a dish.
Total Carbs - 5g
Fiber - 1g
Net Carbs - 4g
Shallots
Shallots are a sweeter style of onion. They provide a more delicate flavor.
Shallots Cooking and Substitutions
Total Carbs - 16.8g
Fiber - 0g
Net Carbs - 16.8g
Vidalia Onion
One of the most popular onions is a sweet variety first grown in Georgia. It was named after a city there that hosted a large Farmer’s Market. Vidalias are the style used in “blooming onions” and are usually used in this manner or in onion rings. A whole vidalia is usually around 1 cup.
Total Carbs - 5g
Fiber - 1g
Net Carbs - 4g
Yellow Onion
The staple in many traditional recipes, yellow onions are cut into cubes and plunked along with meat dishes. They’re used in soups and casseroles. They are usually not very flavorful but are quite inexpensive.
Total Carbs - 5g
Fiber - 1g
Net Carbs - 4g