Which quantitative metrics are there of the quality and prestige of journals, and how do they compare? I have seen several different metrics that are applied for ranking journals: Impact Factor, SJR, and H-index.  Which of these is the most useful and robust for comparisons with respect to the quality and prestige of journals?
In short:


Impact factor is the traditional measure of mean citations per year shortly after publication.  It can refer to either the official Thomson-Reuters computation (which has lots of problems), or other competing similar computations.
SJR attempts to improve on impact factor by using an algorithm like PageRank to more heavily weight citations from "better" publication venues.
H-index for journals is just the same as for people, essentially looking for the volume of consistently good work.  The only large place I know of that applies this to journals is Google Scholar metrics.


All of these are subject to manipulation and gaming, all are highly field-dependent, and none are very good actual ratings of quality.  Still, they can be used to get a rough sense of the significance of a venue that you are unfamiliar with.