BSP has been and may continue to be the original way level designers had created maps, they can be a little screwy due to their build reliant nature. Essentially, make a shape, add it to the world, rebuild, and it's there.

Staticmeshes are almost the same, but they are an actual resource that gets stored on your harddrive as it's own resource, or perhaps in a pack of other resources, and eventually into video memory. They can be exported, imported, you can apply textures to them, make them move, give them physical properties, etc... Essentially you can give way more detail using staticmeshes. BSP does work, still, but using more powerful 3d software to produce what could have been BSP is a lot more functional and efficient, perse.



In short: It doesn't matter, it all depends on what you have available, and what you think will turn out better.

Okay, that's a lie, you can get away with generating rooms, and the playable shape of a map using BSP, but definitely not finer details.