I typically use Autoeurope for rental cars. This time I was surprised by the high quote for an automatic transmission. I expected it to be more, but not almost twice the amount for a manual car. I checked Costco, but they don't have a filter for automatic transmission. I then checked Delta travel. Since their hotel rooms are WAY more than booking thru booking.com or thru the hotel directly, I didn't expect a decent quote. Wow, their rate is excellent for an automatic. I thought I'd pass on that they also offer the additional insurance which was $11/day which was also quite reasonable. I think that is far less that Autoeurope's.
I don't know about other AMEX cards, but my Delta AMEX card does not have car insurance coverage in Ireland (also not in New Zealand). Our Chase cards, do, however. I did double check, and I can book a car thru Delta travel and pay for it with my Chase card.
I must admit I'm a little apprehensive about booking thru Delta when I've become so used to Autoeurope. I did use Delta travel for recent car rentals on Oahu and Kauai with no issues.