If your picking a full size 75b I'd say go with the double action with a safety.
Its a heavy gun and will most likely see more range duty than anything, a manual safety is handy there.
If your picking a PCR or one of the alloy compacts I'd say go with the decocker.
I had a 75b SA - it didnt have the flat spots at the front of the slide and its frame was a little different with a beavertail. It came stock with a terrible trigger (rought & gritty). I didnt like it at all for pure accuracy, but it shot very well in rapid fire.