In my opinion (Books/ book chapters/journal articles) all are good provided they are original and the findings are helpful to the common man, at least to a certain extent.
All previous responses are insightful. From another point of view, the number and the age of readers play their role concerning the main questions of the thread.
Thank you for all your answers. For those who focus on scientific books, it is also important to emphasize the type of editing, sole-author or multi-authors, importance of publishing houses, and their indexing.
I think articles in high impact journals is the best impact in scientific production for a professor, where articles are up-to-date comparing to books.
The impact of scientific production for a professor is quite clear in the achievements he/sh can make and how much they can contribute to society. These achievements can take different forms such as publications, books, researches, articles , lectures, moral or material support, etc.
Although conferences are important in congresses and scientific meetings (oral communications, discussions, oral debates...), it appears that only written publications have a more lasting impact, at least in the medium and long term.
Writing a scientificic papers in a highly cited journals is the most useful, but to take part as a keynote speaker on a yearly organised conference could be effective too.
It is crucial that an academic book manuscript gets peer reviewed. As with journal publishing, it is the external peer review process that acts as a filter, to ensure that the final book is of high academic quality.
All of them are important . Articles convert research work done into science & can be cited by others , Books & book chapters can explain the research work in greater detail & conference gives the author to personally present & explain his work to a large audience . Ultimately , the research work reaches a much wider group of scientists .