Personally, i'd start with the London s/b (possibly with the Tir na nOg s/b as a side), move on through the U.K. and TNO sections of Shadows of Europe, and finish with 6WA. It's the progression of information over time that makes the difference IMHO. Plus 6WA filled in or expanded on some of the blanks that the setting write-ups in SR3 main book and SR4/4A core book.