My top 5 pick of "must run" Class IV in Ecuador (in no particular order):
--Oyacachi (this is probably more like IV/IV+ unless you have really low water)
--El Chaco Canyon on Quijos
--Upper Misahualli (if the water is medium or high)
The Upper Jondachi is definitely the classic run of Ecuador but it is a Class V day. As Matt says, it's mostly Class IV and IV+ drops but a full day of IV and IV+ in hard-to-hike-out-of jungle canyon = a Class V day (I think).
Hollin is also a great run. And, if you don't feel like hucking the waterfalls, there is an easy put in below them.
Lower Jondachi if the water was Medium to Medium/High would also be a great option.
Hopefully this helps.
When you are planning next year, you can keep an eye on water levels here: