I love platinum. My engagement ring is 18 ct white gold but when we bought our wedding bands we got 14 ct. white gold, not realizing the difference. So my band has a bit of a yellowish cast to it. But it's probably only noticeable to me. I have a platinum and diamond ring that was my grandmother's. It's gorgeous.
I honestly don't think your diamonds will look larger or smaller though depending on which you choose. Just get what you like!