initial opinion on Madagascar guides
I bought both Hawkins/Safford/Skerrett and Sinclair/Langrand, the former in the Kindle version. My initial opinion is that the Hawkins et. al. book from Helm (2015) is better, though of course that is tentative until I actually see the birds in November!
I looked at their coverage of raptors, for example, since identifying some of those appears difficult. Helm shows many more plumages, especially of Frances' Sparrowhawk, puts confusing species (serpent eagle and goshawk) on the same plate, and gives identification tips in the text that seem more useful. These illustrations seem more natural, but I'll see about that when I get there. (There are disadvantages to having more than one illustrator -- 2 for Helm, 4 for the other. I cannot even find "credits" for who painted which plates, that is not right!)
Most of the comments in the two previous BirdForum posts focus on their dividing the book by islands. There are pros and cons to that, but it seems appropriate for these islands, and certainly would not be a reason for my choosing one or the other.
Thanks again for the advice.
p.s. since you asked, my avatar is an Ocellated Tapaculo. I started using "tapaculo" for names etc. a long time ago, because it's amusing that it means "cover your ass", more or less...