The reason Twins sucks compared to Teacher is because there was more than just first love at stake in Teacher. At the end of Teacher, Mizuho could lose her job (both at the school and Galaxy Federation) or even serve jail time for infractions of Galaxy Federation laws, and Kei could DIE.
At the end of Twins, one of the girls has to give up her romantic ambitions for Mike.
Gee, I wonder who has it harder? (yes, that was sarcasm)