I like them on its own. I think it's prettier, but if you get another diamond band and wear it with your T&Co ring, it will look very nice. Do you mind me asking how wide is your diamond band? Also, is it a eternity band as well?
Looks to be 2mm or even a little less. I don't prefer symmetry when wearing more than one ring so I like it with or w/o your Tiffany's ring. One on each side takes away the fun to me