Perfect fifth
It's the most stable interval and the Beginning of Star Wars.

I like the fifth too, but octave is just as cool.

Out of habit, I find myself throwing in and resolving suspended fourths a lot. Lately I've been doing a lot of seconds.

... FWIW, Star Wars first interval is a first, the first jump is a fourth (G - G - G - C -G - F - E - D - C - G - F - E - D - C - G - F - E - F - D). Star Trek's first two intervals are fourths. (C - F - Bb then A- F - D - G - C, so there are two more fourths after the reverse arpeggio of the Dm chord.)

As a harmonic interval, I like the major 7th because of its piquancy,and its use in a number of juicy chords.

As a melodic interval, I find I use a lot of rising perfect 4ths and since I am a fan of the lydian mode, I also use a rising augmented 4th with frequency. (love that dominant sharp 11 chord).

2 major chords set a tri-tone apart (the "Petrushka") sound has a satisying color to me.

Sometimes it's not the distance between the roots, but the spacing and inversion of the chords that creates its special character.
F'rinstance, in the "Rite of Spring", Stravinsky uses a root position E major chord, with a 1st inversion Eb7th superimposed over it . (the famous "Stomping Dance"). Listen to the difference if both are in root position. Totally different color.

Being entirely facetious, any when the bar is accessible.