For a “budget” trip, and less than a full week, Iceland will be a better choice. While Iceland isn’t necessarily cheap, Norway will be more expensive. And Iceland’s more compact than Norway, so you can cover more of it in 6-7 days than a tiny portion of Norway. Besides Reykjavik, there’s the “Golden Circle,” with a sampling of volcanoes, waterfalls, geysers, and glaciers. Take a tour (or perhaps drive) along the southern coast for more scenery and natural wonders.
Having said all this, we’re going to Norway this September, but we’ll be there longer than just 6-7 days, for a longer experience. We visited Iceland a few years ago for just about a week, and it was amazing.