And I’ve been to my fair share from Nicaragua to Nigeria, Thailand to East Timor, Easter Island to India, etc; so, don’t let web hype convince you of the best places to go – because there’s 1000s of choices!
However that said, the islands of Cambodia are worthwhile – until mass tourism arrives, which it will, so get there soon.
4K Beach is awesome – for now (in 2016, only a couple of guesthouses on the entire beach but I see on the web that things have developed further).
How to get to Koh Rong Island
Regular high-speed and slower ferries leave from the mainland at Sihanoukville a few times per day. Prices for fast boats are $10 one way.