Reply to Novation Sl MkII 25 vs american audio wms4

Ehy....just looking for some help..my budget isn't so high but i want to take a controller so as to control traktor pro.
I have a mixvibes and a behringer djx 700. I believeed to buy a novation sl mkII 25 too use as a controller (the mapping is not a problem for me...i have done it for my axiom). But many friends told me that keyboards is a shit to that purpose...so the second option is the american audio wms4....but i am not so sure cause in that way i will not use anymore my soundcard and mixer...(And also i will take the novation to use it with ableton). Help me please cause i don't know what to do....if you have also any other suggestion about other controller just say something!!!thanks