Prior to getting my invite and using Inbox by Google, I tried everything I could download from the Play Store for my other mail accounts while using the provided Gmail client. I ended up choosing Blue Mail for all my accts.
Now on day two with Inbox despite it lacking a single unified inbox choice, it's other features are of great value to me. Considering it's a new product with more improvements and additions coming I'm particularly impressed. The layout is very conducive in increasing the speed with which i can process my mail.
I cannot overstate the value of dedicating time to read the tutorials. Some of its best features are easy to use, yet not so easy to discover without learning this app.