So there is more than just style to think of. When setting the stone in a mounting with width, or any shape which does not have at least one totally flat side, be aware that when you go to choose wedding rings this may be an issue. Whenever possible, look for a jazzy engagement ring which already has a matching wedding ring available for purchase. Most women hate having a gap between their rings, so addressing this problem when you buy the engagement ring mounting will save you headaches and unexpected expense later. Here's some advice for the groom who is unsure of what color rings to buy.
Some women wear more silver than gold, some more gold than silver.
Some women want all their jewelry to match, some like to mix it up. Make a point of dragging her along when you get a watch battery changed, or when you want a ring of your own re-sized or cleaned. Go where there are lots of bridal sets on display, and window shop with her. Don't tell her what YOU like, pay attention to what SHE likes. Check out the big store AND the small shops - you'd be surprised at how much money you can save with a little patience.