I think either green or blue will look good on your brown eyes. I don't wear contacts on, but I have seen some girls who wear contacts and find the blue or green lens very nice on the brown eyes. I also find an amber or green lens blends better on a dark brown iris.
Ok, it seems that you would like to get a pair of circle contact lenses to appear to be more attractive. So, as you have a pair of brown eyes, which is beautiful, and your eyes could be compatible with these colors such as grey, green, purple, that is nice, and blue. Anyway, it also depends on your skin tone and your hair color, as well as what you wear. Hope you could figure out what is for you through trying them on.
Regarding to your questions, actually, it depends on your skin tone and hair color. It has nothing to do with your original eye color. Because even though you have brown eyes, the opaque color contact lenses can completely change your eye color. So if you have warm skin tones and yellow-blond or golden brown hair color, contacts that often look best are those that include highlights of light brown, honey, hazel and green.If you have cool skin tones and strawberry blond, blue-black or salt-and-pepper hair color, similarly "cool" eye colors of ice blue, violet or plum may be most appealing.