I'm a clinical psychologist living in eastern Tennessee, USA, and I've been reading Smith since the late 1970s. That first book was "The Sunbird," and I was hooked for life. I've read all of his books and still look forward to each new one, although the most recent, "The Quest," was a major disappointment.
Favorites: "When the Lion Feeds," "The Sound of Thunder," "Men of Men," "The Leopard Hunts in Darkness," "The Angels Weep," "Birds of Prey," "Dark of the Sun," "River God."
Least favorite: The weakest Smith book is still superior to the majority of other novels in the genre (the only other author who comes close is H. Rider Haggard, although he, too, had his share of failures). That caveat aside, I would nominate "The Eye of the Tiger," "Hungry as the Sea," and "Golden Fox" as among his lesser efforts. But there is no Smith novel which is not worth reading on some level.
Incidentally, a very Smith-like novel, one which comes close to the best of Smith, is "Lord of Darkness," by Robert Silverberg. If you like Smith, you're sure to like this one. The writing is superb, the narrative is headlong and exciting, and the characters are memorable, rivaling Smith at his best. I'm not sure if it's still in print, but it's well worth searching out.
Well, that about covers it. I look forward to exchanging ideas with fans of the greatest historical adventure writer of the 20th (and now 21st) century.