As usual with languages, the answer is not 100% black or white, but present simple is the preferred tense to write of an habitual action.
"I collect stamps" conveys roughly the same meaning as "I'm a stamp collector". It describes an established activity. Whether that activity has been going on for long is not the point, as long as it is now an established habit in the mind of the writer. E.g. "Until yesterday, I used to have a job. Now, I collect stamps".
Consider now the progressive tenses:
"What have you been doing this summer?" "I've been collecting stamps".
"Do you want to go out now?" "Later perhaps, now I'm collecting stamps".
In these cases, the verb describes an ongoing activity. But it goes no further than describing what's happening, has happened, or will happen at a certain point in time. It certainly does not convey the idea of an usual or established activity.