Lance has shown traits of Slytherin. Cunning, resourcefulness, ambition. Lance can exhibit aspects of Gryffindor, but I think that’s more Keith’s area: charging headlong into battle and such. At one point Lance had to hold him back from doing so, and inform him of a better plan, so as not to hurt the Balmera. We see Keith do this again in the last episode where he took on Zarkon even though Coran warned him not to, going so far as to switch off his comm so he couldn’t hear him.
I think Keith is more a Gryffindor as he is very brave, courageous, daring and is known to be reckless.
We know that Lance is schemer, and I don’t mean that in a bad sort of way. Only that he tries to think things through before actually diving into the thick of things. We see examples of this also in the Balmera episode. He’s tactical, whereas Keith would prefer to charge in swinging his sword.
NOT that you can’t exhibit more than one house traits.
I’m not trying to shit on Keith, I love Keith almost as much as I love Lance. I’m not saying that these character traits make him a bad person or a bad character. Not in the slightest. I’m just saying. Lance is a Slytherin and Keith is a Gryffindor.