Considering Clementine didn't spend a large portion of The Walking Dead being an unlikeable kleptomaniac that I'd like to slap upside the head, compared to Ellie who did, I think I like Clem better. Not to mention, y'know, Clem shoots zombies in the face after like one lesson. Kid's a natural with a piece. Ellie's got what? Cloaking technology and bricks. Yes, that's another point in favour of Clementine. She never broke my immersion by scuttling around like a crab making god-awful amounts of noise while creatures sensitive to sound stagger about, looking to eat my jugular. Nor did she repeatedly break away from cover and walk through bullets and patches of molotov-induced fire to press her face into my armpits, like Ellie did.
Simply put, Ellie could never be as good a character because she's presented around the game, instead of the other way around. Plus, like I said, she's a whoa-oh edgyyyy kid of the apocalypse so she's fifty times worse than all those douchey pre-teens who wear faux-diamond studded trucker caps and cuss anything that moves.
I mean, let's assume she was raised with or by the Firefly chick that pawns Ellie off onto you. That woman was nice! As nice as you get while blackmailing the only two competent people in the wasteland. Where the hell could Ellie have learned to be such a colossal snarklord?
On the other hand, it's hard to compare the most crucial aspect of both characters: how they react to the apocalypse. It's all Ellie's ever known, so she really has no idea what she's missing beyond the logical mindset of; "Yeah I bet it was pretty sweet when you didn't have to creep around psycho fungi-dudes all the time." So yeah, the way she is fascinated by "old-world" technology and culture is kind of cool, and well-done...but at the same time the cynic in me just sees it as Naughty Dog getting in their shots at taking the piss out of pop culture. Not to say I don't agree with Ellie's little aside about supermodels being stupid for not eating and being so skinny, but really? That's a social comment you'd like to raise in a game about an apocalypse?
As for Clem, she comes right out of a normal life into a living hell. She suffers more, goes through more, and ultimately comes off as the stronger character, quite literally. She's younger than Ellie and never had to toughen up and learn so fast, but she steps right up to the plate and within three months of everything going to shit, she wades through the zombie hordes out of Savannah on her own! Right after her father-figure dies in front of her! In my opinion, she's made of far sterner stuff and is a more interesting character than Ellie.