
to the Forum, I hope we can be some help.
Phi Phi is a pretty Island but the main port area of Tonsai Bay is not the Idyllic Tropical Paradise that it once was. It is great if you want to meet young people and enjoy some nightlife but it is far from the best part of Phi Phi. A quick Long Tail boat ride away from this area will get you to relatively secluded and beautiful beaches and this may be what you are looking for. Most negative reports of Phi-phi will come from the day tripper who only sets foot on the Island at the busiest part of the day and at the busiest area that has just been over-run with other day-trippers.
Railay, on the other hand, consists of one AMAZING beach which is quite small and is very busy during the day, a couple of longer, quite nice beaches where most of the beacfront accommodation is and another beach which is less pleasant, particularly at low tide where most of the bars and a few cheaper lodging options are. Your benefit of staying at Railay is the close proximity to Ao Nang if you want to combine some shopping with beach time but if you want 4 days of Beach Beach and more Beach, Phi Phi would be my recommendation, just get away from Tonsai.