Jayant, I think your distribution channels will get determined by the industry/customer behaviour. If I tell you write articles for
adweek.com, it may not make any sense if your customers don't lurk around there. I've seen that the best answer to this question only your customers can give you as in what sites they hang out on, which groups do they participate in, which newsletters do they subscribe and so on. Sorry for a generic answer but I truly believe that is the best approach.
To add to that you can look for such target websites using a tool like
sparktoro.com, which allows you to discover websites where people of certain interests hang out. You can also use google display planner to identify placements with certain interests. Then just reach out to them, find a mutual fit, write for them, analyse results. Rinse and repeat.