When I did my PPl in the early 90s I used the Trevor Thom books as they were the only ones around. These days there is more choice and personally I feel that the Jeremy Pratt books are the best.
The only book youi need to buy brand new is the Air law book and in the case of the Jeremy Pratt books that book also covers the recent radio changes such as Basic Service.
As for all the other books I don't think in matters if you buy them second hand met, nav etc don't really change that much.