The most suitable reagent for the conversion of R−CH2−OH→R−CHO is
PCC
PCC (pyridinium chlorochromate) is a mild oxidizing agent, which converts the alcohol into the corresponding aldehyde. The mild nature of the reagent helps control and restrict the oxidation whereas the others are strong oxidizing agents. KMnO4,CrO3,K2Cr2O7 help convert the alcohol into the corresponding carboxylic acid.