I have read alot of good things about both. Both tires seem to have excellent reviews and a loyal following. Both are considered high quality, ultra high performance with a solid track record. While I have no hands on experience with the Bridgestone Potenza's, I have run B.F. Goodridge Comp T/A ZR rated tires on my
stang for the last 5 years. These tires provide a very good ride with incredible stickiness to the road. Really inspires confidence in the corners. After reading all the reviews on the Bridgestone Potenza's I am considering those as my next set of shoes for my
stang. I have read alot of good things about one of the Firestone tires also. Trying to remember the name but I'm drawing blanks right now. (I'll update my post as soon as I think of it).
The reason I am switching from B.F Goodridge is not that they don't perform but for two main reasons. I think regardless of price, there are bettter tires out there such as the Potenza's and speaking of price Comp T/A's IMO are definately overpriced for what you get.
In the five+ years I have been running them I have had several blowouts, one of them on a relatively new tire (less than 3,000 miles). This does nothing to instill confidence in their reliability. Besides all that, I have learned their warranty sucks! While I will be moving to a new set of threads for these reasons listed, I would like to emphasis, as far as performance they sure do stick to the road.
Hope this is of some help to you in your decision. Looking forward to reading more comments from others.