I would have to take a guess and say Halley's Comet, but the problem is that during some orbits it gets closer to the Earth than others. The 1987 'apparition' was among the faintest recorded encounters with Earth. The 1910 apparition was among the brightest and most spectacular, with a tail that stretched half way across the sky.
There have been other comets, however, which probably exceeded even Halley's brilliance even under the best of circumstances. In 1811, still spoken of as the "Year of the Comet", a sword-shaped comet graced the skies for 17 months before fading. The size of its head exceeded the size of the Sun. In 1843, a comet appeared in the skies which was so brilliant that it could be seen in broad daylight close to the Sun! In 1858, Donati's Comet also was reported as being very brilliant, and inspired French vintners to establish what came to be known as the 'Comet Wines'. In 1882 yet another comet was so bright that it could be seen in the daytime near the Sun.
Many astronomers think that comet Hale-Bopp due in March, 1997, will also be a spectacular comet based on its sheer physical size.