How did you choose your favorite band?

Why do you have to have a favorite? I have many favorite bands, songs, movies, foods, see what I mean.

I chose them because of the riffs for e.g. System Of A Down was the band that got me into every type of metal.

I don't have a particular favorite but there are a lot of bands I do like. I would say that I decide that by listening to their music and if I like the majority of their songs, then I like that band. If I only like one or two songs or don't like any songs at all, then I can can that I don't like that band.

The Ramones. I can identify with them.

It was easy . The band that had songs I liked the most, more than other bands. Queen has been my favorite since the late 70's. 

I have a few I like....
The Rasmus - 10 Black Roses
https://www.youtube.com/watch?v=4B9FXdL7c2o
Oscar & The Wolf - Strange Entity and Princes
https://www.youtube.com/watch?v=NZRTxlPcNSU
Snow Patrol - Run.......
https://www.youtube.com/watch?v=LdT8hjmFbGg

There is no reason you _must_ have just one favourite band.

Many people like several bands / artists, often in different genres.
There are at least four I like equally - and all very different.

I didn't choose my favorite; my favorite chose me. I just knew they were my favorite band after I heard one of their songs, loved it, and went through the rest of their music and was madly in love with almost every song.

I would suggest not worrying about choosing a favorite. If someone asks, you can say you don't have a favorite or you have a few/several favorites. Someday you might come across a band that just clicks for you, and you'll know it's your favorite. Otherwise, it's nothing to sweat.

I chose my favorite band when I found that they lived in Pakistan