Personally I'd recommend Polychrono. We stayed there 3 years ago and it was perfect for us. Long strip of beach, hotels with pools, plenty of traditional restaurants and bars. Just along the road is Hanioti if you want somewhere more buzzing. We went along a there a cuple of nights and really enjoyed it.
We went self catering to the Kosmar studios (booked through Olympic). They were great, only 12 rooms around a pool, nice and quiet but near to the seafront and main boulevard so perfect for walking home after ouzos!!

Sorry just realised your age - Hanioti might be better!

Hanioti would be ideal for a young couple. There's much more going on here than the other resorts. We stayed in Kriopigi. Nothing there really (well, there wasn't 5 years ago anyway!) we hired a car and visited all the resorts on the peninsular. Kalithea is the best place for authentic Greek food. We ate there most of the time. I had the best squid I've ever eaten, in a little taverna tucked away in a side street. Amazing place.