Which online service to use for airfare refund using EU law?

Do it yourself. I filed that form directly with the airline and finally got compensation in 90days. There is company called AirHelp that wanted to help me for 25% but I was patient.

But what was the reason your flight was delayed?

Which company operated the flight that was delayed?

Iberia online contact form https://www.iberia.com/us/customer-relations/

Better forms from British Air https://www.britishairways.com/en-us/information/legal/flight-cancellation-compensation

You don't mention how many people were traveling, the distance traveled, or the reason for the delay. If the delay was weather related, you may not have a claim. The reason will matter.

Consider carefully if you want to give up 25% of your claim at this point. Assuming a transatlantic flight with a reason for the delay that allows for compensation, you could be looking at 600 euros per person. 25% of that could be quite a bit to pay. Only you know if this is a good value for you.

There was an article in the NY Times about that very recently. I would go to its website and read it. I won't post it here because the article includes a discussion of Brexit.

A lot depends on the reason for the delay. Airlines will try and weasel their way out of payment, I've been successful on two occasions with Virgin and BA doing it myself but it does require a bit of tenacity and refusing to accept their initial denial.

How ironic to see this today. I’m am 9 months in waiting for my British Airways compensation to make its way to me. The flight delay was more than 4 hours, they validated and approved our claim, our travel partners received their wire transfer, and.....we wait. I’ve had numerous emails, several phone conversations and am on my 3rd person, and...we wait. However, I am still not ready to give someone else a piece of the action; I will persevere. My point is, sometimes it goes quickly and sometimes it doesn’t.

Thanks for the post about the article in the NYT - I am going to check that out.

Here’s a link to the NYT article.

Thanks everyone - sounds like tenacity and patience rules, as always.
Our flight was actually canceled due to "technical problems" then rebooked for 40 hours later. So, again, we did get there. It was Iberia's fault, so we will continue with them. BA answered more thoroughly, but were just as dismissive.
I also have complaints about the Iberia staff at JFK, where we waited for 3 hours for them to decide what to do, and then were herded to a hotel with not enough rooms. But that's another letter.

Erica, it is always the operating airline that is responsible for compensation claims. If Iberia was the operating airline, it is not too surprising that BA was not able to give you much assistance.

I hope you will follow through with your EU claim against Iberia( Flight Compensation Regulation 261/2004). Here is a link to a scheduling situation my family found itself in in May and a good outcome. Fill out the online form after reading it carefully with Iberia.

https://community.ricksteves.com/travel-forum/transportation/disappointed-in-hop-operated-by-airfrance-and-will-not-book-again

The delay was at JFK.

Someone double check as it does not look like the EU 261 law is applicable to flights from the USA.

Sorry, I missed that part that it was for an Iberia flight that had the delay in the US. You’re right, the EU regulations won’t apply.

EDIT: AirHelp claims that if the carrier is an EU carrier and the flight leaving the US is to arrive in Europe then EU261 applies. I haven’t read through the Official regulations but it would be important for the OP to do this and then apply.

To clarify, flights on an EU based airline from US do qualify for compensation.