I'm a travel agent and when I used to work for Thomsons they sent me on an educational. I went all around the island. Each resort is different. Obviously you have Faliraki for the 18-30's, Lindos and Pefkos are my favorites. After the educational I took my family to Pefkos. The best beaches are in the south of the island, plus its 10 degrees hotter down there. The island has a waterpark and Rhodes Town is great for a day out shopping (in particular the old town, which is beautiful).
Choose your resort carefully and you'll have a fab time.