You will definitely need a car to move around the island. Public transportation exists but it does not connect all the sites. Big car rental companies are available at the airport or port of Chania (or Heraklio) so you can pre-book online and get your car upon arrival.
Avance – Avis – Hertz – Kydon – Sixt
In case you are arriving in Athens, you can book your car there and take it with you on the boat.
Smaller (and cheaper) car rental companies also exist directly on the island.
Contact details:
Tel.: +30 28210 20823
Fax: +30 28210 20824
Mob.: +30 6944 540825
Tel.: +30 28310 72 440