Just depends on what you like and what you want ... I agonized over red, white, or grey for the longest time.
If you want to be different - go with red or silver...they are by far the most rare colors for BRZs...i see TONS of white, WRB, and blacks and a handful of dark grey and Galaxy blues...
Or if you think you might do vinyl, or change the rims or any kind of mod...i bet dark grey, black or white make for the best background for some colors that really pop :3 (I'd love to see someone do a dark grey with neon yellow/green brake calipers and decals, smoked lights, and blacked out emblems...oops topic of a different thread...)
If you want low maintenance...probably go for grey or silver... dont' see the dirt or dings as much :P
I'd say just go stare at the cars (irl if you can find one...go to a meet-up or something) and pick the one that you can't take your eyes off of and just decide if you can live with it.
(..as much as I lusted after the red one- I decided I couldn't deal with the color on a day to day basis...so I got something almost equally high maintenance
)