The planet in our solar system with the most elliptical orbit is Mercury. The average distance from Earth to Mercury can vary significantly because both planets have elliptical orbits and their distances to each other change as they orbit the Sun.
On average, the distance from Earth to Mercury is about 91 million kilometers (56 million miles). However, this distance can range from approximately 77 million kilometers (48 million miles) at its closest approach (inferior conjunction) to about 222 million kilometers (138 million miles) at its farthest distance when they are on opposite sides of the Sun.
If you're looking for the average distance considering the entire orbital path, it roughly hovers around the aforementioned average, but specific distances can greatly vary.