Best oc for r7 250x ?

I want to make the r7 250x OC and do not know what program to use and that would be the best frequent board, please help: D

Each GPU is different regarding how far it can overclock...

I use MSI Afterburner.

For these cards usually better is HIS or Sapphire software. It has usually wider clock range and sometimes voltage adjustments not available in Afterburner.
Almost every R7 250X will be based on reference design so most of them will offer similar max OC. My card was from HIS and I could make 1200-1220MHz on core.