I need a fighting type for my team, and both Lucario and Gallade seem like good choices. My team besides them is: Greninja, Talonflame, Garchomp, Luxray, and Ivysaur. Which would fit better?
Use Lucario. Lucario has slightly better stats than Gallade, and you get one from Korrina instead of having to catch one. Also, Lucario has a Mega-Evolution in X&Y, and Gallade doesn't get a Mega-Evolution until ORAS.
Hope I helped!
Source: This and This (also, Knowledge)