I am guilty of liking Lucario on aesthetic alone as many casual fans do, but I also appreciate that Lucario is fairly viable competitively as a glass cannon. In addition to having good speed, it also has high physical and special attack, with an ever-expanding movepool to complement those bases. Its Steel dual typing was handy to force Dark type switches in Gens 4-5, while in gen 6 and onward gives it STAB against Fairies, which with a few exceptions all have brittle physical defense.
Lucario was also one of the few megas whose ability made it so broken that Smogon relegated it to ubers and it stayed there. I prefer inner focus to adaptability though.
I also apologize for the mild sperging. Steel is my favorite type and I like my goofy-looking bipedal fight dog. He's a good boy.