Personally don’t like the rifle (not really a fault of the rifle, of course, I just don’t like it, especially when compared to the other choices available)
The Gravigun is just generally fun. The homing isn’t too sharp, but it’s powerful enough to make it actually perform well at range whereas the rifle’s accuracy (at early levels, at least) makes it useful at a distance and uh… not so much at range. At that point I might as well use the shotgun, fan, dash, etc.
The best combo I’ve found, however, is Gravigun + Seeker/Dash. Their playstyles are pretty different from one another but they synergize the best imho. Launcher is a good alternative to Seeker if you find its arming time too slow.
EDIT: so… just learned you can fire multiple weapons at once. gravigun + rifle has to be a war crime somewhere with how fast it obliterates enemies