I rather use stable microRNAs, and preferably more than one, as endogenous controls (using the geometric mean as reference value). One good tool for identifying the most stable miRNAs using your high throughput profiling data is the software NormFinder (https://www.moma.dk/normfinder-software). In that webpage you can find documentation for Excel and R. If you are familiar with the programing environment R, you can include the NormFinder R code in your script or follow the instructions on the attached file (downloaded from the above referenced website). The authors of NormFinder also have a paper (Andersen et al. Cancer Research 2004(64): 5245-5250) describing the statistical framework.