Let her choose (Score 1)

As a geek girl married to a geek boy, my best advice is to pop the question and then go pick out an engagement ring together. She's going to wear it for the rest of her life (you hope), so she's going to want to have some choice in the matter. As well as you might know her, I doubt you can picture HER most desired ring more than she can. Plus, these days a lot of people choose rings where the engagement ring matches both his and her wedding bands. Besides, being asked to be married is so much more the thrill than the ring is.