Popular books tend not to have lots of big words in them, most likely because people seem to want to enjoy reading their books, not expending a lot of effort studying them like a textbook. http://xkcd.com/483/ sums up a related problem nicely, I think.

For story and characterization, I find the Vor stories by Bujold to be good, as is her Falling Free. For well-written stories with a humanist slant, I like stories by Spider Robinson. I'd have to go visit my local library (half of which is down the hall, half upstairs, and half in the garage) for much more in the way of recommendations, though.

I haven't been overly impressed with Asimov's or Heinlein's characters. They are both excellent authors in the SF genre; their stories are well-done and engaging, but I find their characters a bit flat and 2-dimensional. I also think that Frank Herbert was hitting the hallucinogens just a wee bit too too hard when he wrote Dune, but that may just be personal problems on my part. Then again, I liked the characters in Stasheff's The Warlock in Spite of Himself, so take my recommendations with a pound of salt.