It would help in giving advice if you said when going: May? July? September? At any rate here's an alternative view to Laura"s. Yes it IS nice to hire "George's Taxi" but that can cost €500++; what is your budget?? Also, disagree w"avoiding public transportation" is "much less stressful". Of course for an American from Midwest or LA who's never set foot in a bus in a lifetime, "public transit." may be scary. But KTEL (Intercity) busses are not like crowded US city busses. Clean, quiet, reserved, comfortable upholstered seats, A/C, windowshades, swift express travel. And used by ALL levels of society, NOT transport (as in US Stereotype), only the poor.
PLUS actually, travel time on KTEL bus is MORE efficient than tour. Here's why: tour bus may pick you up at your hotel at 7:30, BUT it will spend another hour++ going to other hotels, will not actually leave town till nearly 9. Same at end of the trip. So, looong time on bus, short time on site!! Tour arrives site about 10:30-11, gives you only 2 - 2.5 hours for BOTH the ruins and museum... then drags u off to a taverna for lunch YOU pay for & may not want... then takes you to Arahova (next town) for stops at rug store or souvenir shop (they get kickback for this). How do I know this? From bitter experience my first Greece trip 1999, hated it ... I've been back to greece many times since, finally went again to Delphi by KTEL bus, stayed o'nite had fabulous experience. But you also can have a FINE 1-day experience via KTEL Bus. Here's How:
First bus departs 7:30, so have hotel call you a taxi for 6:30 -- from Plaka district to Liossion KTEL Station, about 20 minutes, €10-12. Buy "Return" (R-T) ticket, Dep 7:30 & Return on last Delphi departure 18:50 (6:50pm). Trip is about 3 hours (brief stop at 2-hr point for snacks/restroom). Nearing Delphi up the mountain, you first see the sites/museum, then modern Delphi, then bus station at other end of the village. Since you have no luggage & already have your return ticket, you can sweetly ask the driver ahead of time to drop you off in front of museum... saves u a walk. You can arrange in advance for a local licensed tour guide to meet you there, Penny is also recommended by my Delphi friend. Usual charge is about 60E per 1-2 hrs ... if you want to do DIY, the ROUGH GUIDE to GREECE has excellent section on Delphi, & here are my fave web links to PRINT and TAKE: 3 best maps/3 best articles
http://www.planetware.com/map/delphi-map-gr-del.htm (the wider area, including town)
http://www.sacred-destinations.com/greece/delphi-sanctuary-of-athena (the "tholos" outside main site)
http://people.hsc.edu/drjclassics/sites/delphi/sacredway.shtm (explan. of ruins on "sacred way" path" )
•The museum (after renovation) has VERY good signage, so u can enjoy it without a guide NOTE: -- go to museum FIRST, because bus groups go fto the Ruins FIRST, so U can enjoy museum without crowds
• TIP -- The stadium is waaaay up top... and a disappointment, hard to see, because closed off (due to rockfalls) U may skip it.
• After Museum & ancient site, Food! Museum has snacks outside, OR picnic on site OR just walk along mountainside parapet to Delphi Main St for leisurely Taverna lunch. What's left? the beautiful Tholos ruin (the round thing, on all the posters), which is steeply downhill from the main site. A clever thing to do, after that late lunch, about 4 PM or so, is to hire a taxi to go down to the Tholos, wait while you explore a bit, drink from the Castelli Spring, then bring you back uphill. Across from where bus stops is a nice cafe w. open terrace & mountainside view, to have a glass o' red & relax ... then you'll snooze on bus all the way home!!