If I had to pick one planet I would say Jupiter because of its exceptionally large size and mass. But all the outer planets Jupiter Saturn Uranus and Neptune are highly unlike Earth.
There are really two kinds of planets in our Solar System. The mostly rocky ones include Earth and three others (Mercury Venus Mars) that are more or less similar in interbal composition. The large gaseous hydrogen-rich ones — Jupiter Saturn Uranus and Neptune — are all so unlike the rocky planets that calling one of them most unlike Earth is really splitting hairs.