Good question! Lite is the best option for most developers since it offers a faster experience for end users; instant email account access when they sign up, webhooks that fire more quickly when an event occurs on the email account, and more. If you need to query indexes, 2.0 will allow you to quickly search through historical messages, get a list of contacts, etc. The main difference between the two APIs is that 2.0 stores more data.
Your API key can be used for either version.
Still not sure which API to use? Contact support@context.IO and we’ll be happy to help you figure it out.