Some practice for marriage... (Score 1)

Use this as an opportunity for marriage practice. Tell your beloved your thoughts about the question, including the fact that you're not sure what you would prefer. Ask her to read some of the stuff you've read, and let her think about it. If she decides she needs a diamond, because of upbringing, or childhood dreams, or whatever, do it, using some of the less unsettling purchasing options (antiques, canadian, etc). If she doesn't, go out and either alone, or together, pick out a wonderful engagement ring that she can be happy to wear forever.

This is precisely what I did with my then future fiancee, and current wife. We talked about it, and she actually turned out to share my unease about the production and marketing of diamonds. So, we spent a day in town, looking at rings, until she found one she wanted, and we bought it. It was a very good sign, I think, that we were able to talk, and agree, and act as a couple.