I'm going to Thailand for a working holiday, and will start off in Bangkok. I've heard a bit about traffic in the city being bad, but how does this stack up against the freedom of having your own vehicle?
I wouldn't buy a car. Thailand is THE worst place to drive. Public transportation is the only way to go in Bangkok. I ride a motorbike in Phuket and use the car only when it rains.
Yes, the traffic in Bangkok is especially bad and road accidents are the leading cause of death among foreigners in Thailand.
Public transport is generally good, but there may be some areas that would be best reached by car - hiring a car might be best in these cases.
Have a look at our Transport and Driving in Thailand and Getting Around in Bangkok pages for a better sense of what you'll be dealing with.
Good luck,
Xavier