The cheapest trip from Raja Ferry to Chaweng Beach

I have a question. Me and my girlfriend will go to Thailand and also to 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 package tours in 12GO asia or is it better to simply take a ferry from Surat Thani to Koh Samui and then take a taxi or Songthaews?

Thank you 🙂