Hi, glad it's of use.
To my mind the 'best' overall study of the legend is Stephen Knight's 'Robin Hood: A Complete Study of the English Outlaw'
https://amzn.to/2WYTtZc which came out some years after both Dobson & Taylor and Holt. Knight pretty much kick started RH studies as an academic discipline in the 90s.
It depends what you are looking for, Holt's book was really the first modern serious study from a historicist viewpoint (the version with the Gest included in the back is its most recent iteration but otherwise unchanged since the second edition of 1989). Dobson & Taylor start from and pretty much stick with the literature, reprinting many of the texts featured on the Rochester site I linked to. Knight covers both, but very much from a perspective that what really matters is the legend (in all its manifestations) rather than its (possibly) historical source.
Needless to say there are countless websites and other books which cover similar territory with varying degrees of accuracy and sanity. Some of the 'fringe' theorists can be frankly completely bonkers.