I'd be more inclined to go traktor, since you have a certified mixer. I've never used rekordbox, but basically you've got a bunch more options in traktor and serato. My advice is to download the demo, and see how you like it.... also, there should be mappings available for your mixer, so no real need to buy a controller as well. check each of their websites, and check the features lists and also the demo videos. this is such an open book question, but really it's personal preference because they all have the same end result.