What is the best protocol for RNA isolation from whole blood? TRIzol or RNA Isolation kits?

I have been trying to get good quality RNA for qPCR from whole blood. The purity and the yield isn't great for cDNA synthesis. Since these are clinical samples, sometimes buffy coat containing WBCs are stored in RNA later. What is the best way to recover good RNA? Use direct blood or first isolate buffy coat and then proceed?