I prefer soybeans. They have more fiber (including more soluble fiber), and they have more protein.

I realized this when tracking micronutrients with an app (tracking every gram I put into my body), and realized my 600 calorie steel-cut-oats breakfast was often outdone by soybeans I'd eat later in the day. The soybeans had more fiber.

And I think they're easier to eat. It's pretty boring, but I microwave a bowl of frozen soybeans and then just eat them plain. They're clean, you could eat them with your fingers without causing a mess (I use a spoon though), and their cleanliness means I'm comfortable having a bowl next to me at the computer or wherever; if they spill I would just pick them up with my fingers and that's it.