VVS1 or 2 is useless in a ring - that means the inclusion can only be seen under a scope! Who the hell is going to look at your ring under a scope? VS1/2 is visible under a loupe - still not going to be going around work or a cocktail party with a loupe checkin' out da bling!
If you can find an SI1 or 2 with the inclusion in the "right" place, a good jeweler will make it disappear. If you have one near the surface, and you can hide it behind a prong on the setting, you won't be able to see it without unmounting the ring. It won't affect the fire in the least, so you can purchase much more diamond this way.
The only thing that matters in a diamond is the "fire". It's the way the light is refracted inside the stone. What goes into creating that "fire"?
First is cut - without cut, color and clarity are worthless. Fire is the internal refraction in the stone, and that is the result of a perfect cut, which subscribes to the proportions for the type of cut, and makes sure no light leaks out of the stone. In addition to the cut, you want to make sure you do not have a culet. "No Culet" means that the diamond forms to a precise point at the bottom of the stone, and it is not broken or chipped off. Inspect this carefully on loose stones, as a stone with "No Culet" on it's rating card can develop a culet if it is not handled properly. This will result in a noticeable dark spot in the table of the ring, as light will leak out the bottom.
Second is color - obviously a perfect D (colorless) will appear brighter than some piss-yellow Z color. But really, the GHI class of color (near colorless) will produce 99.9% of the fire for 1/2 the price of a D stone. Compare them side by side, 2 stones of equal specs, but one D and one H - you will be hard pressed to tell them apart until you put them side by side on a piece of white paper.
Last is the inclusion - obviously a big black chunk of raw carbon or some other impurity will ruin the fire in the stone. But a small inclusion, even one barely visible to the naked eye, will not reduce the fire of the stone.
I'm not a gemologist, but given a pile of stones and an hour or so, I can usually pull out a bargain. My wife's diamond earings were picked by me, and unless you know where to look, you can not tell them from sets costing 10 times as much. And you'll need a loupe to see the differences.