I would suggest something like this.
These were purchased from the Snap-On truck that delivers to my shop. Fortunately I don't need to use them to trim Baku's nails (I use a fingernail clipper that we got while in Japan for that).
This is an old set that I use around the house, but they are incredibly sharp and the main cutting section (at the base of the handle) opens very wide. I could probably take the tip of my finger off if I was into that sort of thing.
I'm not sure if you can tell from the picture but it's a rounded surface that you're cutting with, on both sides. It allows a wire, or in this case a nail, to stay where it is and get cut.
My name is Jon and my wife is Manami.
Together we have Baku, our gorgeous Pit. He was born 7/20/09.