We did an Alaska trip with REI. Food and accomodations were the best available (in Alaska, sometimes choices are limited). There were maybe 12-15 in our group. Guide was very nice and organized. I would go with them again. Tour was exactly as described on the website.

If you are looking at Italy, highly rec Girasole. They do mostly private tours, but are reasonably priced. We have done 3 different trips with them.

In South America, recommend Tropical Nature Travel and Southern Explorations. Both are great, delivered what they promised plus more.