Well it is a personal experience but when I arrive at Bangkok Airport (Suvarnabhumi or Don Muang) I am really not in the mood to take public transport. Most time I will have luggage with me and sometimes I have been flying a long haul.
Really taking a bus or Airport Link? And then change to BTS / Skytrain? Or walk the last part? Really? OK if the prices would be like in my home country I would consider this but a taxi in Bangkok starts at 35 THB and a ride to downtown Bangkok will costs you about 200 THB on the meter. So total damage will be about 200 THB + 50 THB Airport charge + 120 THB Tollway = 370 THB. I most times I do this alone (1 person) but if you are with 2 this costs about 185 THB per person. So you really want to save yourself the price of 1 beer after flying 10 hours? Enjoy life, relax and take a taxi!