Does anyone know if a 4' high retaining wall would be better using railroad ties or cinder block?

If it is for garden property then I would think railroad ties would be better.

Railroad ties, I would recommend, because of the fact that they are treated... to within stand different types of outside abuse...
With strong force those center blocks would crack and break and deteriorate over time. I work in landscaping and most of the time that is what we use is the railroad ties.

It all depends on the need, the desired appearance and the construction. Four foot is not very high for a retaining wall. I have seen 4" high cinder block retaining walls built without motor stand the test of time. I seen other that should be torn down and rebuilt. Note that it is not the earth behind the wall that exerts so much pressure on the wall, it's the water pressure. Good drainage and weep holes are the secret.

I would not use either. The ties will take years to rot but they will eventually rot. The cinder block (cement block) will not stand up well to freeze thaw cycles. I'm in NW Illinois and we use limestone block.