I'd use derogatory because I don't think derogative is a word.

Dictionary.com says this about derogative:

adjective. Tending or intending to belittle: deprecative, deprecatory, depreciative, depreciatory, derogatory, detractive, disparaging, low, pejorative, slighting, uncomplimentary.

Both derogatory and derogative are words. 

Similar in meaning but derogatory intends to be injurious whereas derogative intends to belittle.