Q: Which is easier to publish - an original research article or a review article?

A review article is generally more difficult to publish for the simple reason that it is more difficult to write a good quality review than a good quality original research paper. A good review is not just a summary of the existing literature; it has to be really critical and should provide a direction or perspective for future research. This perspective often develops with maturity and long standing experience of working in the field. In fact, some of the best reviews come from well-respected experts in the field.

However, it also depends on the kind of review article you are planning to write: for a narrative review or a literature review, expertise and experience is more important. If you are planning to write a systematic review, you need not be an expert in the field; if you have a good question, and if the review is properly performed, your article will be of good quality. But then again, a systematic review takes a lot of time. 

If you are thinking in terms of easy publication, I would say an original research article will be a better choice than a review article. However, remember that what matters the most is the quality of your research and how well you have presented it in your manuscript.