many factors affect the results, is you will make relative quantification ???? if yes, it is not matter to use one step or 2 step due to you compare between samples, just make sure that your test is working good..... i think 2 step is good cheapest option ....
You want accurate and reliable results, then you should choose a two step protocol. Besides we are working with the protocol that synthesize cDNA using a common stem loop primer for all miRNAs and later using a specific forward primer and probe for quantification of specific miRNA. By that way you can cut the cost of your consumables to half provided you use a larger test samples. Plus you can save your cDNA for testing other miRNAs in future.