In the JPL Horizons there are
Earth mean equator and
ecliptic reference planes. The ecliptic is an apparent path of the Sun's motion as seen from Earth and tilted 23.5deg with respect to the Earth equator. So, both ecliptic and equatorial planes are directly connected with the Earth.
If I calculate the trajectory of a satellite relative to the Sun (let's say, flying to the Mars) is it appropriate to do it relative to the plane, connected with the Earth, and specifically, the equatorial plane? Is there an other plane, which is more appropriate for calculations of interplanetary missions?
I know, that any reference frame may be chosen for calculations (even with the center in Vesta asteroid), however for any case there is always the most appropriate reference frame exists.