I'm torn between two. The original Callaway Big Bertha was such a game changer. However, the Odyssey 2-ball also revolutionized putters and how many clubs have the popularity the 2-ball does 15 YEARS after its introduction?
It's interesting the various ways this question can be interpreted. Some assume the question is asking about Callaway/Odyssey clubs they currently own. Some interpret this as limited to Callaway/Odyssey clubs they've owned now or in the past. Some assume this asks about your favorite regardless of whether or not you actually ever owned that club.
I've been sing about XR and CF16 clubs so much lately, but I have to go with the XHot 3W. Has inspired so much confidence in a 3W for me which is the toughest club for me on the top end of the bag.