A comparison is made for the helium and argon dielectric barrier discharge, in symmetrical electrode configuration, and on the plasma-induced effects, under He and Ar gaseous environment, on polypropylene and poly methyl methacrylate films, selected as polymers bearing distinct structure, functionality, polarity, degree of oxidation and crystallinity, thus allowing an analysis on the role of plasma active species created in inert gas environment in the surface mechanisms and assessment on the discharge efficiency in surface treatment. It is shown that He allows more fine tuning of the discharge parameters and control over the discharge energy, offering overall a larger range of variation both for plasma conditions and surface properties. The effects of the two discharges are similar at the material surface, whereas He-DBD induces a higher level of modification within the depth of the material. Although the amount of activated oxidizing species is lower in Ar-DBD, it conducts to comparable surface modification, under, indeed, much limited plasma parameters, which points to the role of oxygen due to residual air. The nature of the polymer, mainly the presence of intrinsic oxidized functionalities in its structure, limits only the overall level of modification, whereas the discharge controls the timescale and the mechanisms. Helium offers indeed some obvious advantages to produce and stabilize the discharge at atmospheric pressure, due to particular discharge physics. Nonetheless, the discharge parameters and the surface properties for Ar-DBD treated samples show a good balance, supporting the substitution of He with Ar for surface processing applications.