What are the mm measurements on the stones? Most shapes (all that aren't round brilliants) can vary pretty dramatically in visible size for the similar carat weight, so it could be that the 1.79 faces-up a similar size to the 2 ct stone.
In general though I think the size difference between 1.79 and 2 is likely to not be very large, so I would go with the color you prefer.
Ovals also can have different facet patterns so I'd also pick based on that, trying to avoid bow-tie, etc.
I can't sleep so here's a little infographic on some different types of ovals. The first three are good ovals, and are very rare. The last oval is what the vast majority look like. The second-to-last (the one on the hand) is the same kind of cut as the last oval, it's just much, MUCH better. A lot of ovals have a bowtie AND mushy areas, and while the bowtie can create big sparkles, it can also look dark much of the time (depending on the exact way that particular diamond was cut) and mushy areas have minimal sparkle (very easy to see in videos, not necessarily easy to see in photographs).
Some vendors like apparently yours ascribe cut grades to ovals but it has never been clear to me that they correlate in any meaningful way to beauty - they seem often to just have to do with symmetry and polish or something.