If that's what you call "evil", I'd hate to see what you call "good". Luna's not as bad as you claim; if it weren't for her, I never would've tried watching Sailor Moon in the first place. That, in turn, would mean that I wouldn't have been inclined to find out more about her on the Internet; most likely, that ultimately would mean that I never would've signed up at Fukufics, which in turn means I wouldn't have found Everypony by way of Crescent Pulsar. ...Come to think of it, I probably would never have created Callista either. Huh. I've got almost 39 years worth of comic strips on my bookshelf that tell me otherwise, DB, and I make it a point to read 'em all yearly. >^_^< Garfield may act like a jerk, but he's still had plenty of moments where he's nice to Jon and Odie. Ditto for Heathcliff: a jerk, maybe, but nowhere even close to 'evil'; I've seen him be legitimately nice without anything to gain from it.
Honestly, I agree with CRB. It sounds wrong to call Garfield evil. He's honestly more a representation of how cats actually are. They can be jerks, but they still love their owners. Though they may show it differently. I'll openly admit I haven't seen much on Heathcliff. So I cannot really put my two cents here, since I know nothing on him.
"Never send a child to fight an adult's battle" That's something mommy has said. Luna put Usagi in danger for no other reason than a place to stay. I like to say for the record that this is Usagi's opinion alone. It's been a bit since I read the manga or watched the Anime.
Garfield's a jackass for the most part but he's not totally evil. He treats Odie sort of like a little brother. He picks on him but has his back when it comes down to it. Although, constantly trying to mail Nermal to Abu Dhabi is pretty messed up. Even if Nermal is a bit stuck up about being the world's cutest cat. I see Garfield as more of a chaotic neutral. As for Luna, and it's been a while since I watched the anime too, I'm pretty sure that she knew the scouts in their past lives so that's why her instincts told her to act accordingly.
Nuh uh. She had no idea who Usagi was in the anime! To be fair to Usagi, er my daughter, it does seem in the anime Luna isn't aware that Usagi is one of the Sensh.
And you know what the funny thing is? Luna, Artemis, and Diana aren't real cats; they're space aliens. Don't know why he didn't cross my mind, but yeah, I'd say he counts. Got a few more to add to the list: Furrball from Tiny Toon Adventures, the protagonist of Eek! the Cat, and Tiger from the American Tail movies. Don't know why I didn't think of that last one; my Mom used to play "Somewhere Out There" on the piano for years.