Siem Reap is the picture people have in their heads when Cambodia is mentioned, and the picture is usually of the Angkor Wat complex.
The entire town is often perceived as little but a multi-lane gateway full of markets leading to temples. And while it is exactly this, there is much more to life there than the shadow of large root systems eating through carved stones.
Siem Reap has become very fashionable, with beautiful handcrafts made at local silk farms, an incredible circus, very fine restaurants, and relaxing spas, dotting the perimeters of the UNESCO site. Teachers can take advantage of living in a tourist mecca and splurge on a bit of the high life after hours.
Phnom Penh has had a reputation for being a little bit dirty and seedy, but in recent years it has also gained a reputation for chicness, albeit a gritty sort of chic. Sure if you drive a motorbike around (and you will) you will not make it very far without a thin coating of mixed dirt/dust and a barrage of strong smells and traffic noise, but it will all play as background to the feeling of your own awesome aliveness.
The loud market bartering and frantic pedestrian crossings subconsciously signal to you moment by moment how well you are doing at surviving and thriving. The food in the city also packs a wallop for the senses, and the whole culture of the city has become centered around its genius cafes and classy restaurants. It is recommended for anyone who likes a bit of a rush in daily living.
These two very laid back coastal areas are perfect for laid-back lifestyle lovers. They both have brilliant beaches and ferry access to islands.
Sihanoukville is the access point for Koh Rong, one of the most beautiful islands on earth, which while not a tourist secret anymore, is relatively unspoiled. Kampot is the departure point for Rabbit Island, which is also exceptionally beautiful. There are other smaller islands in each group to discover over weekends with friends. There will be seafood dinners, moonlight parties, and hammocks.
Of the two Kampot can be a bit more relaxed and attract a slightly older crowd, while Sihanoukville tends to bring in younger backpackers, but of course both attract just about everybody. As jobs are harder to come by in both areas, timing of job announcements may make the decision between the two for you. Expect the pay to reflect the privilege of living in the scenery. Also, bring lots of mosquito repellent and coconut oil, for the native sand flies.