For as long as I've used RSS, I have been using Reeder on my iPhone. Admittedly, I became pretty complacent with Reeder 3's interface.
Unfortunately, the Reeder apps aren't updated regularly anymore and only seem to get love when a new version of iOS is released or Apple makes significant hardware changes (like the iPhone X).
So, I've moved on (for now). I like Fiery Feeds 2 because it provides granular controls of the interface, letting me tweak all the things. Font, text size, padding, and margins to name a few. I recommend checking out Federico Viticci's review of Fiery Feeds 2 if you want an in-depth look at the newly updated app.
The only thing Fiery Feeds didn't have, though, was Reeder's interface. As a creature of habit, I wanted to configure Fiery Feeds to look like Reeder 3, sepia tone and all.
Reeder 3 on the left, Fiery Feeds 2 with customizations on the right
First, I changed the theme to Sand in the appearance settings of the app. You can tap that link if you have Fiery Feeds installed, or download it from the Theme Directory.
Then, I changed the font from Avenir Next to the System Font (San Francisco).
Last, I changed the advanced settings below to finish customizing Fiery Feeds to my liking.
Article List Settings:
Article View Settings:
This made my switch from Reeder to Fiery Feeds a lot easier.