If you really want it to look nice, use marine varnish. Not only will it protect, but if you do it right, it will look amazing. If you are going to carpet over it or something, then just use a quality water sealer like Behr's or Thompson's. I went with marine varnish, 3 coats minimum, and think that it will hold up better than water sealer (actually water sealed it first, then lightlyyy sanded, then varnish). I used Cabot's but make sure you mix it really well, the good stuff is on the bottom.
I talked to a guy that was a wood worker about varnishing. He said to go with like 200 grit between each coat, and then toward the end, go with something super super fine, which you won't find at a Home Depot or Lowes. He showed me some stuff he did, and wow, amazing. I'm sure you can google it and find it out. My father also varnished some wood with a lot of success that I surely thought was bought, lol. He also said the trick is multiple multiple coats with light sanding. Might have gone off on a tangent here, but thought I'd give you something to think about.
