Get a 30% transfer bonus when you transfer American Express Membership Rewards to Iberia Avios
There are identical transfer bonuses on now to both British Airways and Aer Lingus Avios and British Airways are the most common / easy to use and link directly with Qatar so there are few people that would want to transfer to Iberia directly.
They *just* ripped out their award charts to replace with new higher ones and the biggest Iberia Sweet Spot of US East Coast to Madrid in business class off peak for 34,000 Avios is now 40,500 Avios and at peak times it’s now 50,000 to 59,000 Avios. This is the 3,001–4,000 mileage band.
This still remains about the only award you would book with Iberia (you may find other instances where Iberia remains cheaper on its own metal) but keep in mind the biggest flaw of the Iberia program:
Award travel on partner airlines booked with Iberia Avios is non-refundable!!
That said, generally you want to move your points to British Airways first for the most flexibility – since you can move from there to Finnair, which has some great redemptions, or Qatar.
See this post on the transfer bonus to British Airways Avios for more on the Finnair program.