There are (really) hundreds of posts on this forum about how to proceed when you are buying (first or upgrade) controllers.
There are a few steps to follow and at the end you should have one or two candidates left that will fit your needs and just pick from them.
1) Determine your (desired) workflow. What kind of DJ are you/do you want to be.
2) Determine what software best fits that workflow.
3) Set a budget (don’t do this at the end, it’s a sure ticket to spending more than intended).
4) Select a max. of 2 controllers that support your chosen software and have the features that support your workflow best.
5) Get some hands-on time on those controllers if possible and then pick one.
You see, in your example (MixTrack Quad and DDJ-SB) you already compare two controllers you shouldn’t be comparing. One is 4-channel, the other 2-channel.
If you did the above steps, you would have come up with one of the things your workflow needs, it either needs 4-channel or it doesn’t. If it doesn’t, why bother yourself with the extra things that you don’t need. If it does, why even consider the SB.
And even if you have narrowed it down to a final choice out of 2, nobody can make that decision for you. If your options are all serious controllers, like the two you mentioned and a few others we have on our shortlist, then it boils down to personal preference.
So my advice is to search the forum for posts on picking a controller and get to work!
.
