I guess I'll share my overall thoughts on who's win.
Garou's Advantages/Win Conditions
Garou starts out with superior AP and Lifting Strength, and when you tie that in with his absurd skill, analytical prediction, instinctive reaction and combat techniques, he'd dominate Danny in close combat. He also has better ranged capabilities but his main win conditions are forcing Danny to waste to much energy until he reverts to his human form or using his BFR. His reactive evolution will counter Danny's and his resistances will be enough to counter Danny's ice, heat, electricity attacks, and his resistance to sound will protect him from the intense sound of Danny's Ghostly Wail. His senses should also allow him to know Danny's location if he's invisible and even if not, he's got instinctive reaction so he can dodge attacks he can't see.
Danny's Advantages/Win Conditions
Danny's ghost physiology protects him from Garou's passive radiation, and his gravity based abilities. It will also give him various ways to avoid Garou's attacks (body control or intangibility), that along with his sheilds which can reflect attacks and this Danny can temporarily absorb powers from attacks that hit his sheilds (within reason) an example being how Vortex's lighting bolt hit his forcefield and it gave him all of Vortex's weather capabilities (tornadoes, blizzards, heatwaves, and storms). Danny's main win conditions would be similar to Garou in the way of outlasting him since Danny's RE can extend his stamina which is already pretty good. Other than that, possession would be the way to go as it has several layers and effects the body (molecular level), mind, and soul. Due to the new updates, ghosts can hit the soul and mind too but Danny actually hitting Garou with a blast... not happening.
My Vote
I'm going to give it to Garou.
His overall fighting skill/capabilities will allow him to stay on top in close combat and pressure Danny into staying intangible and thus wasting more energy faster than Garou would waste stamina. He's got the ability to handle most of what Danny can do and dodge what he can't tank. Danny's reactive evolution is powerful but Garou's is better, and while Danny has good hax, landing it is the issue. I find Garou would have an easier time landing his BFR while Danny is in a tangible state easier than Danny landing his possession (cause let's face it, Garou's to skilled to be hit by Danny's simple punches and blasts). Finally, Garou's overwhelming power might trigger Danny into using the Ghosly Wail which doesn't cause total destruction and while it can mess up a person's insides and negate regeneration, Garou can fight with heavy injuries so even if it lands, it more than likely will do more harm than good. Danny does have duplication but Garou is capable of handling 4 teens who's combat skill pales in comparison to him, the best they could do is help set up a possession.
Note: I didn't include Garou's power mimicry since ectoplasmic energy in Danny Phantom is an energy from a different dimension and he'd need to change his physiology into that of a ghosts which to my knowledge he can't do. And pretty much all of Danny's stuff is a product of his ghost physiology/ectoplasmic energy.
