You are talking about buying a new computer and want to play pretty demanding new games. The i3 is little bit better than G3258, but I wouldn't recommend it for gaming in new build.
Only about 80 dollars more, you can get a quad like i5-4590. It's much more powerful and many current and future games support quads very well. Some unfortunately still really don't benefit from quads over duals.
Both of the duals are adequte for now, specially if you don't buy a really powerful GPU, but if later you upgrade the GPU, you probably have to upgrade the CPU as well. It's always more hassle the more components you upgrade.
So, if you don't want to take the quad now, I think G3258 is better, as it's only little bit slower, and about as future...