Last year I had this idea after watching a marathon of Nanatsu no Taizai.

What deadly sin would the Rainbooms represent?

But instead of focusing on basic concepts of sins, I began to investigate a little more deeply into the meaning of these, and in the end I focused on forming with my words each concept that could fit with the personalities of each Rainboom.

To be honest, it was really hard. At first I thought Rarity would be a the sin of lust, but in the second movie and even in the series, she didn't unconditionally seek fame or "power" like Rainbow Dash, and it was hard for me to classify Fluttershy. I had to watch the series over and over again to make a decision.

Although the easiest ones were Twilight/Sci-Twi, Sunset Shimmer and Applejack.

And I must emphasize that this is my personal opinion, if you have any different opinion, you can share it in the comments.