ok im going completly against the topic but FFXIII has the bets cast of charecters for any thing ive palyed, their so well developed and actually seem human with flaws, they actually make mistakes and they have the balls enough to apolgise wimmediatly instead of drawing it out like a plot point
Durarara! Toradora! Code Geass Katekyo Hitman Reborn! Death Note Full Metal Alchemist Higurashi School Rumble One Piece Gintama Tengen Toppa Gurren Lagann Aria Ouran High School Host Club and loads more.
Tenjou Tenge actually has a vast range of good, interesting, well balanced characters...
The author has taken a mature aproach by not trying to make the audience like the 'good guys' and disslike the 'bad guys'; there is always a scenario were the 'good' characters you may be rooting for (as people are often automatically drawn the the mains) are in the wrong, whilst the 'bad' characters can make wise, sensible decisions.
to me, an anime that supports a LARGE to MASSIVE cast and still manages to keep them unique, entertaining, and memorable would qualify as highly impressive. while not necessarily the "best", it does leave an everlasting impression, to say the least.
some examples would be:
- Code Geass
- FMA: Brotherhood
- School Rumble
- Detective Conan
- Soul Eater
- Lucky ☆ Star
- Azumanga Daioh
- Prince of Tennis
Bleach, Fairy Tail, One Piece, and Naruto are givens
its a difficult question to answer, depending on what your tastes are but
Black Lagoon - Great group of dark characters
School Rumble - someone said it best earlier but who wouldn't want to be in this class
Wagneria! or Working! - hilarious cast of misfits and weirdos
Full Metal Panic
the list can go on