Grand tour travel company

Sorry if this is a faq.

We're a Brit couple planning to do two weeks to a month in South America
next April/May, taking in "the highlights". This is a recce. We'll have
done some Spanish before, and after we plan to live in various places
for three to six months each. What travel companies have people had GOOD
experiences with?

Ones we're looking at a CTS - but it's a guided group and more four
star than we would like, and latinamericatravel, which seems to offer a
lot for the money, but has few mentions in groups.

But any pointers are most welcome. The good uns and the ones to avoid.
If you don't want to say publically, please email direct.

Thanks!