Most are going to say 14"...but I would rather run 12". Lots of people want all that stored energy, but all that already stored energy usually gives a harsher ride from coil bind and the coils being compressed quite a bit til launch where they shoot the front end up. I got MM 10" hypercoils up front with 8" out back and they work great for my purposes. I'd say 12" for a street strip.
I have 325lb springs up front and I think its perfect. Its not rough, its solid. Its how a performance car should feel. Everyone says my car rides great and handles amazing. I'd say if pure street only i'd go with somewhere between 250-300lb front spring with bilstein hd's.