It may depend on the possibilities you have, for example, for different instrumentation available (would you like standard qRT-PCR or NGS methods), also different instruments exist and for them different methods of miRNA quantitation (e.g. Exiqon vs. Taqman). Be sure also that the collected blood is processed as soon as possible (EDTA tubes), or collected into stabilization tubes. You should be aware of various normalization possibilities for expression data. Finally, expression of blood miRNAs is associated with miRNAs of many different kinds. Good luck.