We have investigated the aggregates formed by gemini and single-chain cationic surfactants with arginine head groups in dilute solutions by combining SAXS, static and dynamic light scattering, and PGSE NMR techniques. SAXS and NMR spectroscopy indicate that the single-chain homologue forms spheroidal aggregates, whereas the gemini surfactants form cylindrical micelles. The main parameters characterizing the micellar shape, i.e., aggregation numbers and geometrical dimensions, were evaluated from the analysis of the SAXS and NMR data. These structural parameters are in good agreement with those determined previously by surface tension and cryo-TEM studies. Some divergences were obtained using the light scattering technique, in which case the shapes of the aggregates formed by the single-chain surfactant were not in accordance with those obtained by SAXS and NMR spectroscopy.