Brake Pads
I've tried Porterfield R4 pads, TRD (j-spec) pads, and stock pads on the Supra.
IMO, the porterfields were the best for track use (it is a full-race pad) - but I wore through my rotors w/ the R4 pads. You might try the R4S pads for street and occaisional track use, but the drawbacks here are: they're expensive - the R4 pads were $200 for a set of fronts, I'd think the R4S pads are about the same. Also, you'd be compromising at the track. Since I usually bleed anyway before going to the track, I figure I can toss on a set of R4 pads then too.
TRD - I got decent performance from those at the track. I liked the Porterfields better. But they sucked on the street. Took a while to warm up - and eats your rotors too. Also expensive, though not to the price of the R4 pads.
Stock pads - Best bang for the buck. Decent performance on the track too. I was quite impressed. <$100 for all 4 corners. How could you go wrong?
So in summary - I'd throw the TRD pads on if you're heading out to the track - you should bleed brakes anyway - so while you have the car up and the wheels off - you might as well switch pads. But I wouldn't recommend them for the street.
I run around on stock pads, and am thinking of trying Hawk Blues before I head to the track next. Although - I hear they eat your rotors too... Sigh... Rotors are consumables, just like pads...
Maybe one of these days I'll get an AP racing 6 piston big brake kit - or as my friends call it - the BAMFB kit. First B is Big, Last B is Brake... I'll let you decipher the rest of it. Those use Hawk Street pads, and the braking performance is phenomenal. I've had those on a 300zx - amazing.
-Darryl