I have little experience with the controllers but would offer up some advice from a longer-term perspective - if the end game is to work CDJs in a club environment, assume you'll need to end up owning them at some point and budget accordingly (said another way, you shouldn't expect to be able to prep on either of these units and play out on some CDJs at the club - for a thousand different reasons). If you want to pick up either the XDJ or SX to test the waters and see if live mixing is something you want to pursue, realize that if you do decide to keep at it, you'll be upgrading to CDJs before you know it and whatever $ you drop on one of these units will be sunk. I would recommend considering previous model CDJ/DJMs (e.g., my buddy just picked up a used DJM800 + 2 CDJ900s for $3k, which is roughly equivalent to the cost of an SX + Macbook Pro and despite being older models, wouldn't be surprised if you found some of your favorite venues still running this equipment). That all said, there are some that ignore CDJs altogether and simply bring their controllers to their gigs - while this is becoming more and more prevalent and some big-name performers are doing it (e.g., Porter Robinson), be warned there's still a good number of people in the industry that perceive 'controllerism' as unprofessional and associate controllers with novice/beginner DJs. To avoid inciting a riot on this thread, I personally have no objection to controllers in the DJ booth - I've heard some wicked sets come out of controllers and some units, such as the SX, even have features that aren't available on the newest CDJ/DJM combo. Hope this helps.
