There is a lot of confusion as to the various ways of complying with what is – fortunately – becoming the rule in many countries: the free availability of the results of research performed with public funds. Indeed, there are different ways to achieve this goal.
Here is an elementary and necessarily incomplete comparative table of the merits and drawbacks of the various formulas in the current landscape of scholarly publishing. It is just a modest attempt at clarification for non-experts that can serve as a basis for something more elaborate later.

[Click on table to see it full screen.]

The comments are meant to be as fair and objective as possible, subject to improvement. The colors, from green (positive) to red (negative) are my fully assumed subjective appraisal.