OK, you asked my advice/opinion here it is:
Do NOT start with Athens, as if it is medicine you must swallow in order to get dessert (islands)!! It has amazing landmarks that you will appreciate MUCH MORE at end of your trip. ALso "we haven't heard great things from our friends" -- what were circumstances? Visit in hottest part of summer? A one-day rushed tour from a cruise? A random wander by people who have NO prep, or interest in history? One must always consider the source. Here are the main factors we "vets" cite, for saving Athens at the end:
• Athens, like any national capital, is big & bustling; if one is completely new to ANY country it can take awhile to cope. However, after a few days in the isles, you get the hang of how Greece works, you'll be revitalized, savvy, able to make the most of a vibrant city efficiently, enjoyably & quickly and you'll appreciate what you see .. it will be the BEST at the last.
• Your friends may have stayed in a big chain hotel (on points?), where they had to taxi to sightsee. If you stay in acropolis area, you walk everywhere, it's all lovely, almost no traffic, very relaxing! Just as eye candy, see Fab area photo album from RS regular Stanbr: https://www.flickr.com/photos/stanbr54/sets/72157632121475515/ Tell me it's not charming!!
• You really only have NINE days (plus a few hrs on day 1), not 12 -- and every hour is precious. Much more time-efficient to connect immediately to flight to an island. Even so, You’ll have to limit yourself, realistically, to 2 islands plus Athens. Otherwise, your holiday will be a blur of check-ins/check-outs, waiting at port/airport, getting on/getting off.
The best flight connections — tho most $$ — is Santorini (a 50 minute trip) on May 20 OR May 27 y08 can connect at 15:40 (3:40) or 17:15 (5:15pm) From Santorini there are daily 2-hour ferry rides to either Naxos or Milos … for return to ATH by plane there are late-afternoon flights from both Naxos & Milos on Sunday May 27 or June 3… thus giving you 2 full days at the end (3 nights in Athens. CAUTION - do Not Dither about booking flights, remember this is Bridezilla season, and once these flights are gone, your logistics become impossible.
Some possible Scenarios and Plusse for either Naxos or Milos:
SANTORINI (3-4 nights) - NAXOS (-4 nights) - ATHENS (3 nights)
NAXOS has best hikes on offer – Also, 10 miles of golden sand beaches all in a row reachable via excellent bus network,– one beach directly next to port town, walkable to all sights, cafes, nightlife, a good place to stay Late may, not overcrowded – in a 1-day car rental you can see dramatic landscapes, mountain villages, vineyards etc – Naxos also has day-excursions enabling you to see BOTH Delos and Mykonos & be back for sunset
SANTORINI (3-4 nights) - MILOS (3 -4 nights) - ATHENS (3 nights)
MILOS has TWENTY-TWO different beaches to explore, car needed because bus system is lame – If you want nightlife & big choice of cafes etc, best to stay in/near port town (Adamas), otherwise Pollonia is lovely village on a beach - BIG treat: group day-sails around edge of island, half-day or full day, swims & BBQ in coves, views of remarkable volcanic formations
PAROS? You could substitute it for NAXOS, it has many enthusiasts & I've been there at least 4 times ... I find it harder to get to best beaches via bus, the beach next to port is mediocre IMO, and port town & area not as interesting/attractive as Naxos, again just my opinion. Naoussa (village) very "picturesque" but to me seems like a movie set, again IMO. I"m a great fan of Antiparos, wonderful charm for even short (2-day) stay, completely walkable, the evening scene at harbor and down its Agora (market lane) can be magical.