Sine Mega Evolution is locked to post-game, you're not going to be able to use Mega-Lopunny, even if you traded over a Lopunite. When just comparing Tauros and regular Lopunny, there's very little competition. Tauros has higher Attack and Speed stats. I would suggest these moves:
Take Down (level 35) / Thrash (level 55)
Zen Headbutt (level 41)
Smart Strike (TM 67, received after completing the Lush Jungle trial)
Rock Slide (TM 80, found on Route 17) / Stone Edge (TM 71, Seafolk Village Pokémon Center)
I would have suggested Earthquake instead of Zen Headbutt, but the TM isn't available until postgame. If you can and want to, you could trade it to another game with the TM then trade it back.
Here's a comparison of the two.