Hey so based of the title you may wonder what is the true way to choose a BTS Bias. So I will explain. 

Through the period of a year and a half, I have finally discovered the most fair and pure way to chose a bias in BTS (you can use this method for other groups also) without feeling guilty about leaving you past bias or stuggling between 2 memebers (or if you're me 7 members). This is how to solve it (I'll make the steps work for any group): 

Steps:

1. Buy the most recent album from that group. 
2. Open the album. 
3. Find the photocard if there is one (if there isn't, well, darling you're screwed until that group releases a album with one)
4. Also, if the album has a version or a poster of a certain member (Ex. all Sm groups) then they are also your bias (if they have both a photocard and a member version or like 2 versions, then you'll get to choose betwee them or just go with both) Also note this, if the group does have single member versions, chose random to make sure it is fair. Same goes for posters. ALSO, if your an Exo-L (#me) I suggest using the Korean version (because it's k-pop). 
5. That person is you're new bias until the next album. 

AND WALLA. You now have a bias. Now if you're leaning towards a certain person already, but you'er not quite sure then don't fret. You can always get em' next time. So now I am going to tell you how this has worked for me. 

I already have a bias in every group (I'll write a list) besides BTS, so this method obly works for them. SO BTS' recent album is HwaYangYeonHwa pt.2 (well actually it's young forever but I haven't gotten it yet sooo). I got both versions (blue and peach). Now this is my small flaw. I got J-Hope in one album and the GROUP PHOTOCARD in the other. I say go with what ever cover is more used. SO in this the blue is more used and I got the group photocard. So basically I have no bias until I get the new album. 

Also if you don't want to get the album, I suggest choosing out of a hat

I hope this helps you.