I am an AZ Millemiglia member (although I never use the account) and considered joining Frequence Plus but decided to stay with Delta for the following reasons:

1. I would not be able to get comped for my current GM status.

2. My ability to get miles from partners would be much less with AF or AZ.

3. They do not offer bonus miles for Elite level members.

If I were to leave Delta, my move would be to AZ. Firstly, I fly it more often than I do AF. Secondly, after reaching Elite level (45,000 miles) I am allowed entry to their VIP clubs and an excess baggage allowance of 10 kilos. Thirdly, unlike Delta and AF, AZ considers Israel to be in a "Europe 3" category, meaning that a r/t to the US costs 50,000 miles, not 80,000.