I'd say that the best intro book on CT is a pair (\P,\B) where \P is a problem (in algebra, topology, logic, computer science, whatever) in resolving which you are really interested and suspect that CT would be useful to approach it, and \B is a set of chapters taken from a set of CT-books/papers that you suspect is reasonable to read to approach \P. Normally, it'd work as follows. Having \P in mind, you have some main interpretation of CT-constructions you've read in \B (actually, they have multiple non-isomorphic interpretations) and it'd guide you thru \B (a qualified advice here would be very useful). It allows you to reformulate \P more precisely in CT-terms as \P' and it gives rise to \B', and so on. Hopefully, at the end you'll have read a set \B! and interpret it not only in terms of your problem \P but much wider, with a few interpretations in mind, and in abstract CT-terms as well. Then you may well consider your have some working knowledge of some fragment of CT. Well, for someone some strong curiosity itself may provide enough motivation for CT-studies (probably, there are as many ways to and in CT as there are people willing to follow such a way), but I suspect that without \P CT-studies might be really hard with any \B. ZD