No one can really answer this question for you because it really comes down to your need for portability,
Obviously, going with the iMac 27" removes any chance of going portable. So, if you need portability, the iMac is NOT a choice.
Apart from that, it's also obvious the iMac 27 is a more powerful PC.
Maybe get the iMac 27 now (the fastest Mac ever!) and make some money, then get an the Macbook later. You'll have the best of both!