This is perhaps the most obvious pairing on the list, since the man bun was probably designed to go with a beard. The beard balances out the bun and adds a nice contrast. The hair on the head is in a small bun at the back, and the beard allows the head to be unified as a whole. The same goes for a top knot.
The man bun and top knot also work well with all kinds of beards. Here, stubble is probably the beard style that won’t work that well. A mid-sized beard will probably do the trick. That’s about 4 to 6 weeks of growth, depending on how fast your facial hair grows. This is also often the type worn by most guys who aren’t going for the clean-shaven or lumberjack looks. It’s right in the middle.