It is best to own one or more of these as often there is a different approach. However you should at least know one book well. I have found that Kumar has gotten bigger over the years and has almost become a reference text. I like Patrick Davey's (Medicine at a Glance) book a lot with the diagrams and explanations. Davidson's continues to be excellent and is another very good choice and despite the fact that it appears smaller it is packed with information.

 I like the crash course book in Medicine and its very easy to read from cover to cover. I have all of these books (you certainly don't need all !) and each one is excellent and at the end of the day it's a matter of personal taste. The hard work is not in choosing them or buying them but in actually studying them