Both are really good, but I can't add anything onto the "Portal 2 for more quality" and "New Vegas for more value for money" sort of thing going on in here already.
Edit: Given that you need to decide between one or the other tells me that maybe you don't buy games too often, so many NV would be the better choice to tide you over until the next time you have some money together. That said, Portal 2 has pretty good co-op stuff, and just got community maps too. So it still has al ot of potential if you're into doing a lot of puzzles.
Edit: Given that you need to decide between one or the other tells me that maybe you don't buy games too often, so many NV would be the better choice to tide you over until the next time you have some money together. That said, Portal 2 has pretty good co-op stuff, and just got community maps too. So it still has al ot of potential if you're into doing a lot of puzzles.