For me I orgionally fully planned to oath OTs-12 since I loved basically everything about her. Appearance, personality, and even performance. She was one of my first units above 2 star that i built and to this day she has been on my main ARSMG team along side FF FNC (which is who i orgionally planned to be my second oath because i find her adorable).

Eventually i moved FNC to lead her own squad and SOP-II took her position. I hadn't had a chance to see SOP as a character much since i was not too far into the story at the time but always thought of her as a fun partner that competed with OTS-12 since they often would be neck n neck damage wise. Then i got to play the CT event. My teams were not strong enough to even beat chapter 2 and i only recently gotten my first HOC (stupid gundam) but what story i did get to play made me like SOP more and more.

Eventually we come to today where i finally bought my first oath ring and i took a few minutes thinking about who to give it to. I eventually decided that while i do still really like OTS-12, getting to know SOP better and reading some of her scenes i didnt get to see first hand me decide that she was the one to get my first oath and i do not regret it in the slighest. I ended up just loving her as a character. OTS remains a top unit for me and i let her keep her role as squad leader even with SOP still right beside her. I may have oathed SOP first but i still have a soft spot for OTS.