Where to describe the pros and cons of the related work in a paper?
One criterion is how important these comparisons are for understanding your work.  At one extreme, you may be writing a paper whose sole purpose is to address a gap in the literature by doing something in a better way than other papers or using different hypotheses.  In that case, nobody can really understand your paper and its purpose without an explanation of how it relates to these other papers, so you would need to discuss this in the introduction.  At the other extreme, you may be mentioning related work only for completeness or because it might interest the reader, with no necessity at all for understanding your paper.  In that case, you might as well not clutter up the introduction with it.  Most papers are somewhere in between these extremes, in which case you'll have to make a judgment call (and may end up with a compromise, such as discussing some related work in the introduction and other papers in a section of their own).