Hmmm... I never thought about this. it'll definitely include the original 5, and Chomper, but who else?
After much thought, here's my top 10:
1. Ducky-my favorite character from the start, I've loved her optimism, her catch phrase, and her species (Parasaurolophus, the swimmers!) I remember wishing that she'd eventually star in a movie, and then she did (#8), and I hated it! It was so sad seeing Spike and Ducky fall apart. Still, she's my #1 by a long shot.
2. the sailbacked lizard that keeps appearing in the opening intro of films- Alright, I know there's no proof that it's the same lizard each time, but wouldn't that be cool if it is? Whatever he's doing is always a visual metaphor for the opening dialogue, not to mention it usually ends with him barely escaping ingestion by some sharp-toothed scoundrel!
3. Cera-My favorite aspect about Cera is how she's incredibly self assured, and I like female characters who stand up for themelves. She's also the skeptic, bringing her toher firends back down to Earth whenever they spiral off on some emotion-induced path (like, let's just cross the gorge and see what happens, or, what if that newcomer guy is actually the Lone Dinosaur!?!?) Lots of times, I find myself seeing a hole in somebody's agrument, only for Cera to voice it on screen seconds later.
4. Littlefoot-the de facto leader and protagonist of the series, Littlefoot is the one that needs to take his friends opinions and ideas, and decide which hold water. He can't be overly believing like Ducky, overly critical like Cera, or overly mute like Spike

, he needs to be the happy median in btween. And, most of the time, he does it quite well.
5. Ali-The female equivlent of Littlefoot, Ali is just as nice and quick-thinking as he is, and a perfect foil for Cera. She also matures greatly in the course of her one movie debut, overcoming her xenophobia and holding her won specal place in the one adventure she went on. It also helped that Movie #4 is my 2nd favorite.
Movie #7 is my favorite, making the next character:
6. Pterano-One of the best crafted characters in the series, Pterano is one of the few anti-heroes the series sees; he tries to do what's best, but can't see past his own short-comings. He eventually redeems himself (Saving Fave Character Numero Uno from a very crushing death), and recieves something that, in my opinion, not enough villians recieve, a tangible punishment, in his case, banishment for 5 years (definitely foreshadowing a reappearance in the later movies). Add the British accent, and you've got a really awesome character.
7. Chomper-I wasn't sure about the placing of Petrie and Chomper, who should overshadow whom, and finally decided that Chomper was more likable than Petrie. A very brave character, who is willing to adapt to live with creatures he would normally hunt; a loyal character, remembering this friendship 3 movies later, and helping his friends survive on a strange Island, and the one protagonist with a very curious problem to overcome; his diet of meat. This will certainly cause problems in the future (though it's unlikely they wil be addresed in any film), and I'm curious as to how Chomper will overcome it.
8. Petrie-A lovable flyer, Petrie is seemingly less mature than the other main characters (even Spike has better grammar), yet still provides invaluble support in many situations (though if he wasn't the only one with wings I doubt he'd serve much usefullness at all). While watching the movies, I slowly picked up the Petrie/Ducky relationship, and was thrilled to find others commenting about it online. Despite the strange interspecies problem it would cause, the pairing in my idea sounds wonderful (the small ones do need to band together, especially with what they go through every movie). Still, he annoys me at times, which is why he's ranked so low.
9.Spike- Spike is a really underdeveloped character, which is part of why I've ranked him rather low. His inability to speak has caused him to become little more than a taglong, albeit a taglong that provides transportation for the smaller ones of the group while Cera and Littlefoot are free to figure out problems up ahead. I really wish he'd show more emotions, diffucult as it is for silent protagonists to do so, but the well-developed other characters usually make up for their static counterpart.
10.Mr. Clubtail- While his status as a background character makes his no worthier than last place on my list, he still makes the cut, due to his continued apperances. other than relatives of the 5 main characters, few adults ever continue to make appearances in the LBT movies, and Mr. Clubtail is by far the most common of them. While his gluttony and grouchy attitude makes him little more than comic relief, he still partakes in most of the important events of the series, and emerges unscathed, not to mention he's usually the first to back Cera's dad up when he starts accusing people and heightning the conflict. I always look for him in the fringes of large scenes.
Sorry I wrote so much; it's hard to cut the writing down when you've put so much thought into it.