DMK is served by only a few airlines and amenities within the airport (as in food) are limited. Transportation possibilities do not include the train. On the road the tolls for this portion of the highway are the most expensive in Bangkok (60THB).

However if you're in the western reaches of Bangkok DMK might be easier to get to and the flights out of there tend* to be cheaper than those out of BKK to domestic locales.

I much prefer to deal with BKK but occasionally I'll head over to DMK when the flight schedule demands.

*This is often true with DD and sometimes true with FD.