They both have their place. Carey has more complete discussions of concepts, but I agree with some others above that it is awful to read straight through. March, on the other hand, is more like a collection of one-sentence snippets of chemistry. It is easy to be misled into thinking that two methods of achieving a transformation are equally important, whereas in reality one is much more prevalent in practice. March might give each of these two methods a single sentence and a reference. March does have an incredible breadth of information though, so I actually use it quite a bit more often than Carey now.