Best guides to buy?

We are planning a trip to France this year and wondered which site/travel guides are best? 

Although we have travelled in Europe before, just not in the past 5 years. 

Also I see lots of people seem to talk about ACIS and camping cheques, what is the purpose of these.

Previously we have always gone in high season but now retired we can travel anytime, although keen to go when there's a good chance of sun! Prob June?

Any thoughts would be welcome thanks all.