While I've enjoyed every Character Meal that I've done to date, I've only done them for breakfast so I don't have much insight into lunches and dinners, but I would recommend either Goofy's Kitchen at the DLH or Minnies & Friends at the Plaza Inn inside DL.
My Goofys experience is in my September '09 report Day 3 I believe and my 2 Minnie experiences are March '09 Day 3 and September '09 Day 4.
They both have their pros and cons. I really, really loved the character interaction at Goofy's over Minnies and the fact that I could eat there and still have time to reach the gates before the Park opened was a huge plus. It also had a wider variety of food available as far as the buffet went. On the other hand, what I love about Minnie's is that it is inside Disneyland itself which is beyond cool.
It also depends on what characters you want to see. At Minnie's I've seen Minnie, Fairy Godmother, Max, Captain Hook, Br'er Fox, Tigger, Eeyore, Pooh, Chip and Dale ... I feel like I'm forgetting someone. And at Goofy's we saw Goofy, Pluto, Baloo, Chip and Dale, Jasmine, and Cinderella.