How Often Do You Change Civs?

Just wondering how often people switch it up, primarily in 1v1?

I used to play only random Civs then decided to focus hard on Mongols.

Then I focused hard on Bulgarians for like 4 months.

Berbers I've been playing for a couple weeks and really like them.

Tried Magyars today and my timings are all jacked up.

So how do you pick your Civs?