If you are deciding between Dialogflow ES and Dialogflow CX, here are some rules of thumb you can use.
I recommend using Dialogflow CX in the following cases.
You need to build complex multi-turn conversations
If you use the slot filling and follow up intent features in Dialogflow ES, you will almost certainly benefit from migrating your bot to CX.
You are not building a large FAQ chatbot
While Dialogflow CX is suited for building large FAQ bots, I would say it is not necessary.
That’s because Dialogflow ES is usually sufficient for building such large FAQ bots which answer one off questions, and ES is more affordable.
You are not on a tight budget
Dialogflow CX allows you to build bots which are quite a bit more complex than ES. On the other hand, I would say CX is also quite pricey, especially in comparison with ES.
You don’t require automatic integration with external apps
If you are using Dialogflow ES, you have a lot more integrations with existing apps and external services simply because it has been around for much longer.
This situation will certainly change over time, but it is an important consideration at the moment.
However, you can usually build these integrations yourself by using Dialogflow’s REST API.