You have three options when choosing to make your work open:
All three options will allow you to share some version of your work with the wider world. However, your decision will likely depend on two key factors:
This combination of factors can produce many different results. For example, early-career scholars often have access to fewer research funds or grants to cover publication charges, and often feel pressure to publish in particular journals in order to satisfy tenure requirements. These individuals might choose to publish in a subscription journal and make use of other means to provide access to their work. Scholars who work with translational research and who want to ensure their materials will be available to communities beyond the academy might choose an open access journal to ensure the broadest possible access to their work, regardless of fees. Some researchers might have publication requirements imposed upon them by funding agencies, mandating that they share their work openly in accordance with the funder's rules. It's even possible that a top journal in your field might have very author-friendly agreements, allowing you to publish your work in accordance with open access principles without having to compromise on your need (or desire) to have it appear in a particular journal.
The most important thing to remember is that there are many ways to make your work open. Choose the method that works for you and your co-authors.
In order to make an informed decision, educate yourself about the default copyright policies of any journals you are considering as publication venues. It's possible they have author-friendly policies already. If you have received funds to support your research, educate yourself about any mandates or conditions upon receipt of those funds. It's possible your funding agency has requirements for publishing that you weren't aware of previously. If you need help finding an appropriate publication venue, consult a librarian in your field.
While open access has allowed more transparent access to research, it has also spawned a cottage industry of fake journals who exist for the purpose of generating revenue rather than to further scholarship. There are a few simple steps you can take to avoid being fooled by a "predatory publisher."
The best defense against being duped by a predatory publisher is a strong understanding of the publishing landscape in your own field. To learn more about where and how scholars in your discipline share their work, contact your librarian.
[This material was adapted from Meredith Kahn, "Sharing your scholarship while avoiding the predators: Guidelines for medical physicists interested in open access publishing," Medical Physics 41, no. 7 (July 2014), http://dx.doi.org/10.1118/1.4883836. Licensed under CC BY 3.0.]