I think either a ring or a pendant would be lovely!! Here is a picture of my oval amethyst ring. It''s 2.5 carats and is set in YG with small pave diamonds on the sides. A little smaller than yours but may give you an idea of size if you set yours in a ring. I have a larger oval amethyst(10 Cts) which is set in a pendant. I love it too! I think it would look great either way.
I would set in a halo pendant, similar to this. I want an aquamarine and ruby pendant just like this. Unfortunately, I have no one giving me 3 ct stones! Whatever you do I''m sure it will be beautiful!
Well, treystar, a lot depends on your taste in jewelry. Speaking for myself, I would say that a 3ct. amethyst would be too small to set in a pendant unless you had a halo surrounding it or some metal to give it bulk. If you are artistically inclined, you can even do a search on the internet and get some ideas of how you can set your amethyst in a pendant made of sterling silver or gold in a fancy heart shape or something abstract and use it as a focus stone.
If your fingers are dainty, on the other hand, a 3ct amethyst would look perfect as a ring with or without pointers.
The original example where all this started rather far out of this world (here)... then the reasonable tube-set piece at DBL came up and perhaps this sort of thing would work out.