I think a lot of the replies are on point.
I personally think you should look at how you want to DJ, and then think in terms of which setup gives you the closest match. Try out demos, play with them, and don’t worry if you make mistakes.
Right now, I usually lean on the top titles…because I’ve been a victim of buying setups and then watching them be discontinued. I bought Final Scratch, and then watched NI and Stanton split. I bought Deckadance to replace Traktor DJ Studio in Final Scratch, but watched it wither away. I bought Torq, and again watched AVID discontinue it after 2.0.
Now I have Traktor…mainly because I feel they would be the last company to kill their product line. If I didn’t go there, I’d go Serato or VDJ. MixVibes is worth looking into, but I fear they might fall down the same path.
In regards to controller options, you will get way more options with Serato and VDJ. However, I would not rule out Traktor as being “NI only”. I’ve used a M-Audio Xponent (and an X-Session Pro) up until a month ago with Traktor, and now I’m using the Behringer CMD components with Traktor. Some manufacturers will offer mappings off their website, and if not there are loads of mappings on websites like TraktorBible and DJTechTools.
So try stuff, and if you want to change, don’t worry. Ebay makes it easy to sell off old gear and get new. Go play and find your niche.