Which credit card should I use to purchase proposal/engagement ring?

ALL THE BEST FOR THE UPCOMING PROPOSAL!

Given that it's a higher value purchase, definitely try to rack up either the miles or cashback on your card! It really depends on which jeweller you are intending to purchase from though.

On a slightly related note - maybe don't spend so much on the ring. I always had the thinking that with prudent couples, they would just get a simple ring/wedding. If decades later, when the relationship really stands the test of time (and by then, savings would also have grown) - then splurge on a nice ring/holiday/party if you like.

When I see couples break up within the first few years of marriage, I always think back on the extravagant weddings and proposals and wonder if it was worth it.

Depending on the vendor you purchase the ring from, some jewellers may actually impose an additional charge if you pay by credit card. In such cases, I would advocate paying by cash. If not, either use the Amex true cash back, or if you are in the miles game, you may consider a miles card with a decent sign up bonus, of which there are quite a few in the market now.