There are three major companies in the Monteverde/Santa Elena area that do canopy tours. Apparently Aventura features 16 cables and a Tarzan swing, so that's on my list for next time! But I stayed at Pension Santa Elena, which pushes SkyTrek. I don't know anything about the third company.
SkyTrek features 11 cables and a few suspension bridges, plus for a few more dollars you can combine it with Sky Walk, a short hike that crosses several suspension bridges. You can also pay with credit card, which was important to me because I was low on cash!
Sky Trek is at the Santa Elena Preserve, although not technically inside--that's not allowed. It was so much fun! May be less enjoyable if you are afraid of heights or don't enjoy roller coasters. You wear a harness and hook onto a long cable...one of them was 800 meters long! With a little push from the guide. . . you're flying!
The feeling was truly exhilarating. At one point I saw a bird flying below me. Some of the cables went through trees, which the guide called "George of the Jungle lines." One cable, because it was rainy season of course, went through a CLOUD. It was pretty crazy, everyone got soaked and couldn't see a thing. . . but the idea that we just flew through a cloud was amazing!
The Sky Walk is a better way to experience the forest, although it's not technically in the Santa Elena Preserve either. You start by climbing a very high tower, the same one that starts the canopy tour. You go at your own pace. The bridges are scarier than the ziplines, but there's just no comparison to normal hikes. . . they are suspended hundreds of meters above the cloudforest floor! Definitely try to do both if you can.