I have both the Fiskars Oval cutter and circle cutter. I never liked the oval cutter much. I found it hard to use. I always had trouble getting the position right, and also keeping the cutter in place for the entire cut. The circle cutter is easier to use and I did use it for a while, but I don't use it much anymore. Now I use the Coluzzle templates for both circles and ovals. I find them much easier to use and it's really easy to see exactly where you're cutting.
Hope this helps!