Most of them fit the bill, because there is a prominent love triangle, but in most I either didn't mind who FL ends up with or never had a SLS, This is my opinion only, I can be quite weird, unlike most I've never had SLS with Cheese in the Trap for example :-) Some of them have mild "evil" characters, but they are more annoying rather than anything and sometimes even help the love triangle with their presence.
Cunning Single Lady
Go Back Couple - Had a MAJOR SLS, hated ML
Fated To Love You - ML is in love with somebody else at first, but she mistreats him and he falls for the FL before the drama is halfway. This drama has some angst as well.
My Secret Romance
The Greatest Love
Love Alarm
Discovery of Romance - got confused who is the ML and who is the SML in this. Also there is another girl who is in love with one of the MLs, he sees her as sort of a sister, but she does cause misunderstandings.
I second School 2015 for an enormous SLS , but this drama has some darkness in it
High School King of Savvy I don't remember much from this drama, but it definitely had a very prominent love triangle. I think many had a SLS.
Go Ho's Starry Night - reverse harem, a fluffy short drama
Flower Boy Ramen Shop