I've been to Argentina 3 times, each fishing a different region. I recommend this book because I have read it and find it to be generally accurate. "Fly-Fishing in Patagonia: A Trout Bum's Guide to Argentina."

For overall fishing (lakes and rivers) I think the area around Esquel is the best. If you are taking wives then San Martin de Los Andes would be the best combo because of the shopping and restaurants. The Rico Pico region is more undeveloped but offers some monster fish in Lagos 1,2,3 but limited river fishing although the baca at Rio Corvocado gives you the opportunity to catch some nice fish.

Be warned: You will want to stay, the women are beautiful, and the steaks are worth the plane trip alone.

Feel free to pm me if you want places to stay and names of guides