I always take cash and have a credit card only as back up.
I keep it on me in a secure inside pocket while I am travelling between locations and lock it in the room safe when I get to a location. You then dont lose on conversions, dont pay commissions, dont have to take your passport around to change TC's,and dont have to worry about a machine eating or damaging my card. People will tell you that you run the risk of loosing cash and that is the risk you take, but to this day I havn't had an issue. I have certainly misplaced more cards than wads of cash in my day.

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I love Thailand this much