What is the most reliable way of finding the most relevant publications in scientific field and particularly a specific topic?
Does Google Scholar citing results suffice?
IMHO, it is difficult to say which search strategy is most reliable. The Google Scholar (as well as Web of Science, Scopus, etc.) citations are a good place to start but they definitely should not be your only guide.
Another item to look at are survey papers and research monographs in your field of interest (and, nowadays, Wikipedia, Scholarpedia, etc.; note also that sometimes plain Google search instead of Google Scholar search brings more helpful results) and the references therein.
There are least two reasons to do so:
sometimes an important result makes it straight into surveys and monographs which get cited instead of the original paper(s);
a paper with an important negative result (e.g. one which closes certain research avenues) is sometimes not particularly well cited just because people move on to other research directions.
Yet another way to find relevant references is the so-called snowballing method a good description of which is given at this answer (without using the term snowballing).
And, of course, it is a good idea to ask your colleagues, especially after you've already done some searching on your own and just want to make sure that the search results you have are reasonably complete.