I've been a huge fan of Les Misérables for many years now, and while I do not own every version, I do have both the Original London and Broadway Recordings, and I have heard selections from the Complete Symphonic Recording (CSR) and the Tenth Anniversary Recording (TAR). Before I break it down by character, let me just say that any recording of Les Misérables is worth your money, even the highlight recordings are enjoyable.
Orchestrations - London. The Broadway recording is fuller and clearer, however, it is also a lot more rushed. Now, for certain songs like "One Day More", that works, but at other times it can be a problem. The orchestrations on London seem more refined, they're slower and you have to opportunity to catch more and experience it better.
Jean Valjean - London. Colm Wilkinson is the definitive Valjean, and plays him on all of the recordings with the exception of the Complete Symphonic Recording. On Broadway he is rushed too much, he speaks quickly, and tends to say every word like it is its own sentence; it ruined "What Have I Done?" for me. What makes Wilkinson the best Valjean, while he is good in the TAR, is exemplified in the London recording. He is a wonderful actor, and appropriately conveys every emotion needed for such a complicated character. His voice is full and powerful, and he hits some truly high and difficult notes with such perfection that he makes it seem easy.
Javert - Tenth Anniversary Recording. Philip Quast is by far the best Javert, without any questions. He performs Javert in both the CSR and the TAR tremendously. While the Javert from London, Roger Allam, is quite good, he leaves a lot to be desired, and I have a strong dislike for Terrance Mann's performance on Broadway, it felt weak. What Quast did that was truly impressive, at least to me, was that he took a character I never really liked, and made me love him. I was blown away by his rendition of "Stars" in the TAR, truly amazing. He fills the characters shoes perfectly, he sounds tough and intimidating, a truly complex and interesting character performed beautifully.
Fantine - This is a matter of taste. I prefer Patti LuPone's Fantine on the London recording, though all of the other Fantines are excellent as well. No matter which recording you end up with, you'll get a good Fantine.
Thenardier - London. Alun Armstrong plays Thenardier on both the London and Tenth Anniversary Recording, and he is spectacular. Yes, he does have a cockney accent, which is somewhat confusing since all of the characters are French, but he is still amazing. He performs Thenardier exactly as he should be, crooked, rude, conniving, and just a little bit skeevy. His renditions of "Master of the House" are just fun to listen to; you can see why that song is such a crowd pleaser.
Enjolras - Broadway. Even though I don't think Michael Maguire is the perfect Enjolras as so many make him out to be, he is quite good. He performs on the TAR as well, though he was vocally less than perfect there. His Enjolras is tough and determined and convincing, though Craig Pinder on the London recording is very good as well, and I've never heard the CSR Enjolras.
Cosette - Tenth Anniversary Recording. Now don't get me wrong, I adore Rebecca Caine's Cosette on the London recording, but Judy Kuhn is just a better performer. Vocally I would say the two are equally impressive, but Kuhn really makes Cosette seem so much more real. She's equally as good on both the Broadway and the TAR, but I would give it to the TAR, simply because Cosette sings many of her songs with Marius, and the Marius on the Broadway version is awful. A final note, on the London recording In My Life and A Heart Full of Love are not only lyrically different (and In My Life is much shorter) but they are all one track, entitled "Love Montage" which includes a song not present on any other recording I have seen called "I Saw Him Once". This song is absolutely beautiful, one of my favorites on any recording; it's definitely worth searching for and getting a hold of.
Marius - London! This is not even a question, there is absolutely no debate here, Michael Ball is, without a doubt, the definitive Marius, no one has ever surpassed him. I cannot say enough about his performance, it's powerful and nuanced, and you sense the conflicting emotions that Marius goes through at different parts of the show. His rendition of "Empty Chairs at Empty Tables" is truly breathtaking and heartbreaking, one of the most powerful performance I've ever heard. He is wonderful on the London, TAR, and the CSR, however, I would choose London only because it is the one I have listened to most. The only other Marius that there has been was David Bryant on the Broadway recording, and he is awful.
Eponine - Here is the only character where I'm not sure. Truthfully, I wasn't blown away by any renditions of "On My Own", Eponine's main song and one of the most popular from the show. The three Eponines are Frances Ruffelle on the Broadway and London Recordings, Lea Salonga on the TAR, and Kaho Shimada on the CSR. It really seems like there are four different portrayals of this one character (I didn't at first believe that Frances Ruffelle did Broadway, she sounds so different). I guess this comes down to a matter of taste. Of them all, I guess I would have to go with Frances Ruffelle on the London recording, her "On My Own" has an understated elegance, and it's quite beautiful, though Kaho Shimada did an excellent job as well.
As for the other smaller characters, Young Cosette is enjoyable on all the recordings, as is Gavroche, though the boy who plays him on Broadway for some reason bothers me. I guess if I could suggest only one recording, I would have to go with the Original London Cast Recording as being the best overall. Though some of the songs have slightly different lyrics (including "Stars", "Drink with Me," and "On My Own") it is never a problem, and you have to remember that the London recording was the first, and it is truly spectacular.