Shinra tensei would have an overall wider range of devistation, but honestly all it does is push away, on a planetary scale it would only push the planets away right? I mean they wouldn't be destroyed from shinra tensei. Large areas would be destroyed by shinra tensei on the planets but wouldn't destroy a planet like kamehameha would Kamehameha would be able to hit from a farther range though since its a beam and shinra tensei is spherical. While shinra tensei could cause mass devistation to planets by moving them out of orbit or some shit, he could just blow up the planet with a kamehameha easily. Both are powerful both are devastating. Whatever 1 trillion ki means, i'll assume it is relatively large and is enough for shinra tensei to **** up a solar system's orbit, where as a kamehameha wouldn't be able to do that since its a beam and wouldn't really be able to take out all the planets at the same time. But then again a kamehameha could probabally take out a star which would **** shit up... and it's damage would be more instant.
I'll go with Kamehameha, Its damage is more instant and can potentially hit stuff at longer range. Think of Kamehameha as a Gamma ray burst that is being fired at planets while Shinra tensei is a supernova explosion that pushes instead and doesn't explode, but rather messes up gravity and stability of life of a solar system. Both have power and can hit for vast amounts of area, but the gamma ray burst can travel farther and perhaps hit more planets, thus causing more damage.
ANYWAYS, (this is completely off topic) Goku should just learn tri beam. I think Roshi actually describes the kamehameha as piss in comparison (or something like that, but puts the kamehameha to shame that's for sure).