I think it comes down to how you want to use the software. I chose Traktor because I used it in the past and felt comfortable with it. However, that one gig I played in Slovakia they had me use VDJ and it came quite easily for me since DJing is like riding a bike with these setups.
I will say with VDJ, you’ll have a bigger selection of “ready” controllers over Traktor, as you’ll have to find mappings or make mappings to use with Traktor, or stick to NI hardware.
I found this page on the VDJ site trying to explain how they stand out. They claim that Traktor has become more about integrating DJing with live musicianship, while Serato is more focused on turntable-loving DJs, thus painting VDJ as a title more suited for DJs who mainly want to play sets. I don’t know if I agree with their assessment, as you can go in many directions with all the big titles.
Best advice is to download some demos and try them out.