Wiggum wins for me because he's such a hilarious wimp and works best as a standalone character IMO. For example we've seen Wiggum interacting hilariously with the world around him, in moments like these:
But I don't think we've seen the same with Lou or Eddie because they're not as direct parodies as Wiggum is. (Even if I don't know exactly what c. 1920s-'50s cop characters Wiggum is parodying, I feel like I understand his archetype well).
He sees the world with giddiness and glee like Homer.
Lou comes across as kind of bitter but rule-following. I feel like I "get" him; he seems straightforward.
But, in particular, I feel like I really don't understand Eddie as a character. The only way I could describe him is "normal", mysterious, and tough, really. That doesn't give me much to go on.
I don't feel like I can imagine them outside of work very well.
Okay, fine,
some redditor saw Lou and Eddie off-duty once
, but still.