Rafting in Tena is widely considered to be some of the best in Ecuador - certainly better than that in Baños, if slightly more pricey, but believe me, having made friends with a lot of rafters in Tena and done it myself, it's worth it. There are five companies offering rafting trips at the moment in Tena, all within a block of each other by the bridge. What could probably be described as the daddy is Rios Ecuador. Set up for more than a decade now and part of a chain which runs rafting trips throughout Ecuador, they now run trips with an extremely friendly team, usually led by Tarquino, who has excellent English and will be sure to make your trip very enjoyable. That said, they are pricier than other groups, going from $50-$65.
Another excellent group is The River People, set up by one of the original Rios Ecuador team it is now a family business, with the father, both sons, and one of the daughters active in the company. Originally from England and, more recently, Ireland, the family moved here as missionaries in the early nineties. Naturally, they have excellent English and are all extremely friendly. They used to run a cafe as well, and the result is an excellent lunch on your trip, a step above the others. Expect to pay around $45. Lenin Cerda is extremely friendly and runs a very good, if slightly less friendly trip, as often the guides don't speak English very well. That said, he himself is very friendly and does run a very good trip often at $40 if you can push him down. The two other companies include Aqua Extreme, who suffer from inexperience, slightly higher prices, and a lack of great English, but make up for it in enthusiasm, and a fifth company with an orange front, next door to Aqua Extreme, is also extremely new and tends to specialise in jungle trips rather than rafting, so it's best to avoid them. Enjoy your trip if you go. Hope I can help.