To me, it's gotta do everything; go fast, turn fast, and stop fast. It also needs to have creature comforts (power windows/locks, AC, and a stereo). For me, there's nothing better than wailing around an on-ramp at double the posted speedlimit and having enough power to merge with no issues whatsoever.
And then, when some asshat cuts you off, you have enough braking power to toss your passengers through the windshield if they're not wearing seatbelts.