It depends on how the story is written. If the ML created trauma or did something I can't forgive I usually root for second ML.
If the story is the typical jerk and protective ML but good guy second ML, I usually root for ML.
I like it when the ML teases the MC.
Usually 2nd ML don't tease but are plain good guys with nothing going for them except being extremely good.
I did mention jerk ML but I meant the typical romance story ML that treats the MC like a goddess. Not the ML who is a jerk all the time and treats the MC like they are trash. In those scenarios, I not only root for the 2nd ML but I also abandon the story alltogether.
There's a huge difference between "ooh he is a bad boy that teases me" and "he is a trash ML that abuses me mentally and possibly physically".