I have guided both rivers commercially in rafts, although it has been 10 years since I was on either one. As said before, the Apurimac has much tougher rapids than the Tambopata. It is primarily a whitewater trip, although the canyon is gorgeous. It is much, much more difficult than the long Idaho river trips with lots of big drops and several long portages. The river is super high this year (right now anyway) and it is a pretty serious raft trip. I wouldn't go with just any outfitter - I can only recommend Amazonas Explorer and Apumayo. People have died on this run.
The Tambopata is one of the more remote rivers you can run in the world, and it also has fun whitewater. It is more like class III-IV. Water levels fluctuate a lot, and the river can double or triple in size in a matter of hours if it is raining in the highlands. The Tambopata is more of an expedition into the Amazon Basin than just a whitewater trip, although the whitewater is fun. You start by driving across the altiplano near Lake Titicaca and then cross a pass over 15,000 feet before dropping down into the cloud forest and the jungle to start rafting around 3,000 feet. We had tapir walk through our camp on one trip and saw a jaguar by the river on another. You can end up at the Tambopata Research Center, one of the best jungle lodges in the world for wildlife viewing with a world famous macaw clay lick Can you tell i like this trip? I took my 12 year old nephew on the trip and he went on to major in Spanish and became a Class v kayaker and raft guide. I think he had fun on the trip.
I sell both trips through my company Detour at www.detourdestinations.com
. Give a call (number on the website) and ask for Greg and I'd be happy to talk to you about both rivers.