Personally I like Yayul better, he loved her for a long time and dedicated his life to be by her side and protect her, they share the same mentor and are both underdogs who like staying in the shadows. Most of all they're both on equal footing. When they interact it's not all business and scheming, it's actually caring words and bonding.
Also he is the one that killed her in her previous life so he is the only one she is connected with since before dying and also I'm a sucker for the enemy to lover trope.
But all in all I think I'll drop this manhwa the moment she end up with the tsundere-with-0-chemistry boy. Even Jegal is 100% better than him.

Maybe because we haven't seen Ryucheong actually do sth, but Jegal feels like a much better candidate tbh. He knows how Yeon is, willing to help her, they even have exchange crucial information about themselves under the tree. The only down side of him is he's terminally ill and will likely die
The romance arc is gonna be painful. We know the ML is Ryucheong anw but I hope the storyboard do it justice for these children's feelings. And Yayul.. damn, Yayul, idk what to do with him honestly lol