It still matters a bit. If you're in New York, for example, you can transfer Amex points to ANA, then redeem for flights on Star Alliance partners. Since ANA's reward chart is mileage based, you could get business class for 68,000 miles per ticket (100,000 for first class), if you could construct an itinerary that is under 9,000 miles. If you're leaving from the west coast, it would take more miles. If you're going to be travelling more than 9,000 miles, Aeroplan probably becomes a better option - they have access to the exact same award inventory.

If you transfer to anyone besides ANA, the miles required don't change like that, but it's something to take into account.

You could get excellent value (and a great travel experience) by transferring to a *A airline (probably Aeroplan or ANA) then redeem for flights on a *A partner (SWISS, Lufthansa, etc.).