Not Luan - those April Fools episodes are the worst. To be fair, most eps focusing on Lori aren't any better...At least recent episodes focusing on both are them actually becoming GOOD characters, so I can't stay too mad at either. However, they're not my favorites.
Best / Favorite sisters: Luna, the twins, Lucy, and Leni (in no particular order, either.)
And I don't need to remind anyone that Lincoln and Clyde by themselves are weaksauce/terrible characters, compared to whom I prefer to watch this show for, including Lori and Luan, as at least they are getting better.