We report an extensive set of quasi-elastic light scattering measurements of the hydrodynamic radius R H of aggregating polystyrene latices. The experiments have been performed in the transient regime in order to follow the kinetics of the aggregation process induced by the addition of a simple salt. We are able to distinguish various regimes of aggregation in different physical situations. We observe reversible flocculation and diffusion limited cluster aggregation (DLCA) in latices of 481 nm diameter, but also reaction limited cluster aggregation (RLCA) followed by DLCA for particles of 91 nm. The growth laws of R H in time have been verified and give exponential RLCA kinetics for short times and power law DLCA kinetics for long times. Both the exponential and the power law behaviors are observed in the intermediate time regime. In the DLCA case, for the largest particles we used, deviations from the asymptotic law have been obtained and can be described in terms of the Smoluchowski model for Brownian aggregation, together with the fractal nature of the resulting aggregates.