Largest, most massive planet

Jupiter

Smallest, least massive planet

Pluto

Fastest orbiting planet

Mercury

Slowest orbiting planet

Pluto

Most eccentric orbit

Pluto

Most circular orbit

Venus

Longest (synodic) day

Mercury

Shortest (synodic) day

Jupiter

Coldest planet

Pluto

Hottest planet

Venus

Most moons

Saturn

No moons

Mercury, Venus

Planet with largest moon

Jupiter

Planet w/moon w/most eccentric orbit

Neptune

Greatest average density

Earth

Lowest average density

Saturn

Tallest mountian

Mars

Deepest oceans

Jupiter