A)Pricing.
B)Cooler design: this one can be especially tricky. It's best to find a review of a specific model if you can, because manufacturers do sometimes drop the ball on their cooler designs.
C)Number of CUDA cores, Stream Processors... basically the brunt of the gpu's performance.
The different brands all have their gpus price segmented. Typically, the higher tiers have all the bling and the beefiest coolers, and the lower tiers have less to no bling and barely adequate coolers or loud fans.