Dear Sabrina, we used beta-Actin as a housekeeping gene. The quality of RNA decreases with time.

Best regards.

It depends on the type of study that you are doing. If you are handling FFPE cancer/tumor samples, I recommend that you don't not use Actin as a house keeping genes and instead use B2M, CLK2 or RPLPO 

I've worked with qPCR using breast cancer ffpe tumor RNA.

At that time we evaluate three reference genes (B-Actin, 18S and GAPDH) and the best option was GAPDH since it had a similar expresión level compared to our gene in question.

At the end, and as Leila was saying, it depends on the type of study and the genes you want to analyze. Be sure to make some research to find out the recomended reference gene in regard to its stability across different conditions.