The cheapest flight from Raja Ferry to Chaweng Beach

I have a question. My girlfriend and I are going to Thailand and Koh Samui in January. I wonder what kind of transportation is best to take in Koh Samui and also in Thailand in general. Is it better to book combined journeys on Asia 12GO or is it better to take a ferry from Surat Thani to Koh Samui and take a taxi or Songthaews?

Thank you 🙂