I recently went through the same decision process. In the end I chose the DDJ-T1 because it would most closely emulate CDJ’s, which was a big part of my decision considering that they’re still club standard and I aspire to playing the big clubs some day. I didn’t know the DDJ-SX could be used with Traktor, but that’s ok because I don’t like how they put the platter above all of those pads and I’m not sure those jog wheels emulate CDJ’s as closely as the DDJ-T1’s do.
If you’re still considering the DDJ-T1, you can order from Pioneer directly and get yourself 40% off on a refurbished model. That’s what I did, saved me about $300 over retail.