Of the non [R] Skylines in GT-2, The R 34 is the one that will give you the best HP figures. It maxes at 774, which is about 100 HP more than the chassis likes. Tune it to run the "591's" and it will serve you well and be easy to drive.
My personal preference is the R32. It handles great. Even near max buildable HP it is fairly docile, goes where its pointed...all the good stuff a fast car is supposed to do.
In my experience with GT2 the Nissans, especially the Skylines were the "big dogs". Easiest to build a "Beast" out of. Even the Pulsars are awsome in GT2.
GT 3 is geared toward the Lancer as the "big dog" among the non race cars.