Q. How do you decide which book is best?

Only you can decide which book best suits your purposes! But some good things to look for are:

1) Was it published during a time when your topic was being discussed? For example, if your topic were Facebook, anything from before 2004 would be unlikely to be much use.

2) Is there a chapter or section dedicated to the thing you're most interested in? Never feel like you have to read a whole book when the part you need is ten pages long!