I am planning a trip for end of May for maximum 10 days in Greece.
I will be flying out of Seattle.
I am thinking 3 days Athens, 3 days Santorini and 3 days in Paros
I would fly in and out of Athens. Last that I checked flights to Athens were more frequent and reasonable than the ones going to Santorini
Open to recommendations.
Thanks

I'd think about what those days are going to turn into

Day 1 long haul flight spent mostly on the plane
Day 2 get over jet lag
Day 3 wander around Athens
Day 4 fly to first island
Day 5 get your bearings
Day 6 wander a bit
Day 7 fly to next island
Day 8 wander
Day 9 fly back to Athens
Day 10 fly home

You're spending five of your ten days in airports. Jet lagged at least one more

Early May 2022 my family and I spent 4 nights in Nafplion, 3 in Santorini and 5 in Athens, 12 nights in all, we flew out on the 13th day. On arrival at Athens we picked up a rental car and drove immediately to our Airbnb near Nafplion. Note, we had already spent over three weeks in Italy and weren’t jet lagged.

Back to Athens to drop off our car and our flight to Santorini, we also met my nephew and girlfriend who had flown in the previous evening. Last five nights in Athens, with a long day trip to Delphi.

Three places in 10 days would be rather rushed. Fly straight to one of the islands on arrival and spend 3-4 nights, then Athens for the rest of your stay. You can perhaps make a day trip or two, depending on how long you have.

Late May is a great time for Greece! Weather is warm, and the islands are less crowded than in high season (Jul-Aug). As others have mentioned, your itinerary is a bit rushed, but manageable IMO. Plan your trip according to nights rather than days, as 3 nights mean only two full days at a location. Suggest you book a connecting flight to Santorini the same day as your arrival in Athens, leaving 2-3 hr layover.

Aegean Airlines/Olympic Air allow you to check in online up to 48 hours in advance, so you can do that before leaving home, printing out boarding passes at the same time. That means you can leave your bags at the drop off point rather than joining the queues at the check in counters, then proceed directly to security at the departure gates.

Going to the islands first saves you a day mostly wasted going into Athens, checking into a hotel, and returning to the airport the next day. Save your Athens sightseeing for the end of the trip, which also gives you a safety margin if you are delayed returning from the islands. Santorini and Paros are a good combination of touristy and more traditional. If you just want to see the highlights of Santorini you could reduce that to 2 nights, adding an extra day for Paros.

Paros has a lot to offer, especially when you consider Antiparos, the small neighbouring island, as part of your stay. From Antiparos you can also take a day trip to Despotiko, a small island which has an archeological site similar to Delos. The site is still being excavated, and the archaeological team will be digging in late May. Despotiko is still free to enter, but you will have to pay for the short trip from Ag Georgios on Antiparos to the site. The boat is the same one that takes the team back and forth to the site.

The flights from Seattle to Santorini are way more expensive than the flights of Seattle to Athen . I fly with delta.

Not an issue, book your flight to Santorini with about 3 hours leeway after you ETA. Athens airport isn’t very big and you shouldn’t need very much time for immigration and baggage. Both Aegean and Olympic allow you to check in 48hrs ahead, so get your boarding cards prior to arrival and just drop off your bags at the counter. Then grab something to eat before heading to your gate, easy peasy!

Easy peasy if your flight to Athens is on time. On my trip, the flight into Athens was VERY late. Fortunately, my ticket was NY to Santorini all on one ticket, so they put me on a later flight to Santorini. If it hadn't been all on one ticket, I would have had to buy a new ticket to Santorini (usually expensive when you're buying one for that day).

I am confused.
For example it would be Seattle- connecting to AMS- athens ( stay a few nights ) - then fly to Santorini ( stay a few nights ) and then fly back to AMS as connecting flight and Seattle
I would think this would be all on one ticket

Some airlines will do this sequence all on one ticket IF they are members of some kind of "alliance" (Star alliance?) that includes a domestic Greek airline (Aagean? Sky Express) ... but if not, you can't do that. For example, my local-hub airline, American Airline, does not have that arrangement. It's impossible to discuss these tickets without naming the airlines & the "alliance" involved.

Seattle to Athens would be one ticket. While it's possible for the Santorini leg to be on the same ticket most airlines don't do multi night layovers.

How did you buy this? Seattle to Athens and a second ticket? Or Seattle to Santorini?

I was going with the idea given above to go to Santorini first and put all your Athens time at the end. This saves time and a hotel change.

i have not bought my ticket yet. flying to santorini from USA is very expensive

OK, when I went in 2017 the cost of NY to Santorini wasn't much more than US to Athens plus Athens to Santorini. Maybe that has changed.

Have your priced a one way (or RT) back and forth from Santorini or other islands back to Athens and add it to your cost to/from the US. I'd expect it comes out to be fairly comparable in the end.

Evidently you are flying from Seattle to Athens with a stop in Amsterdam (AMS). From Athens to Santorini you have several choices, including ferries and flights. Ferries are usually a little cheaper than flights, but take longer, and the majority of ferries depart Athens (Piraeus) before flights from the USA arrive.

You can book your flights from Athens to Santorini on separate tickets if you wish. That doesn’t give you as much protection as flights booked on the same ticket, but are often a little cheaper. Aegean Airlines/Olympic Air has a ticket class called ComfortFlex which includes change to an earlier or later flight on the same day for free. Allow yourself three hours layover and you can plan a flight to Santorini the same day as your arrival in Athens with confidence.

As I mentioned earlier it would be wise to save Athens for the end of the trip. If something were to go wrong (weather, strikes, etc) it would be better to have that 3 day cushion in Athens before the flight home. After all, you have more to lose if you miss the flight home to Seattle than the one from Athens to Santorini.

Why not book a flight from Seattle to Santoirni with only 1 intermnedietgen stop, mayy be at Dublin or Heathrow