Which potatoes are best for twice baked potatoes
There are two main types of potatoes: starchy and waxy (although some are considered in-between). The difference, as you might imagine, has to do with the starch content of the potatoes. 

When cooked, starchy potatoes (like Russet potatoes) tend to break apart. They are often used in baking and frying. They also are more absorbent of liquids and fats.  

Waxy potatoes (like red potatoes) hold together more when they are cooked. They are more likely to be used in soups and stews. They also tend to have thinner skins than starchy potatoes. 

Yukon gold potatoes are considered in-between starchy and waxy. Their medium levels of starch make them a good all-around potato. 

But if the Yukon gold potatoes aren't working, I'd suggest using a starchier potato. One of the things that makes twice-baked potatoes so good is that the inside is mixed with other ingredients and then reheated. Starchy potatoes are more likely to absorb the butter/cheese/other ingredients.