We used Aquaventura and were very happy. The guides were experienced and responsible, while still being fun. Once on the volcano we realized that the company was also better equipped than other companies (i.e. gas masks - the day we went there was hardly any wind which meant the fumes from the volcano were too potent to breathe in...95% of tours don't need it, but I'm glad we had them).
If you are only going to Pucon to hike the volcano, be prepared to stay a few days just in case. If the weather is windy, the hike will not go. If you do not have the time to spare, contact the tour company ahead of time and confirm the weather.
Overall, it was a great hike and we would recommend it to fit travelers. Be aware that if the guides don't feel that you will safely make it to the top, they will bring you back down and you will not get your money back. It's not a technically difficult hike, but you should be prepared to walk uphill over volcanic rock and ice for 4 hours (breaks every 30-45 mins).
Bonus: this is meant to be one of the least expensive active volcano hikes in the world.
This review is the subjective opinion of a TravelPod member and not of TravelPod.com.