Luigi likes approaching with fireballs and down+b, the tornado, which gets cancelled out by baby aura spheres I think. He has extremely fast aerials, some that are even faster than Lucarios. His range is easily beaten with the exception of his back-air. Luigis back-air does decent damage and has pretty good range. He's pretty good at juggling floaty characters in air too, but if you DI out of certain attacks like n-air at low percents and u-air, you can escape them pretty easily. He has good killing moves too. Watch out for the Forward Smash tilted upwards, it comes out extremely fast, faster than his neutral Forward Smash. Luigi can approach with a sliding downsmash by simply walking (not dashing), then doing a Down Smash. When he walks towards you, be ready for that. Also, watch out for when he stops a jab, be prepared to shield it. Luigi mains set up an Up-b with Jab - Up-B or Jab - Jab - Up-B. Up Tilts combo into each other into an Up Smash if you have bad DI at lower percents as well. Luigi is also difficult to gimp. He has three moves used for recovery, down b, side b, and up b. When edgeguarding him beware of his side b. It has a 1/8th chance of misfiring, causing over 20% damage and huge knockback if it hits.
Lucario can easily stop Luigi with Forward Smashes which outprioritize his Tornado (I think), and fully charged Aura Spheres. Baby Aura spheres get canceled out by his fireballs. Lucario has more range than Luigi in the air, except with Luigi's Bair vs Lucario's Fair. Approach with aerials, jab-jab-FP, or tilts. If you're cautious, this matchup is in Lucario's favor. He mostly outranges Luigi in the ground and on the air, and if you have decent DI, you can avoid getting juggled into an up+b for upwards forward smash. If he does a side-b on the ground, stop it with an aura sphere, and punish the huge amount of lag afterwards.
Overall, I'd place it at 60-40 Lucario, or somewhat close to that.