I'm in Australia right now, and have been using my Discover card in supermarkets here (for the grocery store bonus rate spending).

I've noticed the exchange rates have been consistently better than I've been getting with Visa and Mastercard. For example:

7 Feb AUD 223.20 -> USD 153.79

The transaction didn't change from pending until 11 Feb, so to make sure I wasnt missing something I checked Mastercard and Visa exchange rates from Feb 6 - Feb 11 for the same transaction (with 0% FTF) as follows:

mcard visa
6 Feb: 155.14 158.15
7 Feb: 155.19 155.16
8 Feb: 156.17 156.01
9 Feb: 156.53 156.19
10 Feb: 155.54 156.55
11 Feb: 155.54 155.41

I've also seen this reflected on other transactions, where the difference between Visa/Mcard always seems to be around 1% better.