Both shows are about a couple of students doing random stuff. they are both very funny and if you enjoy one of them the other will also be enjoyable. The one difference is that Plastic nee-san is about 3 girls and Daily Lives of High School Boys is about a group of boys.
Life is simply not worth living for down and out school teacher Itoshiki Nozomu. He has no hope of progress, no prospect of promotion, no chance at happiness… he is in despair! Even his name spells 'zetsubou' – 'despair', when compressed. But when the time comes to end it all, Itoshiki's attempted suicide on the first day of the new school year is foiled by relentlessly positive Fuura Kafuka. This saves Itoshiki long enough to meet his new class, and the quirky range of students under his care. Will Itoshiki Nozomu depress his students with his anguish? Or will Fuura show Zetsubou-sensei the joys of life and hope?
At the Kaimei Academy three classmates, “Bossun” Yusuke, “Onihime” Himeko and “Switch” Kazuyoshi have established their own club: the Academy Activity Support Club. Known as Sket-Dan for short, the trio accept any odd jobs that come their way in the name of maintaining a peaceful life for the students of the academy. Whether identifying a graffiti artist, fixing the school gym shed or helping a new student fend off his childhood bullies, no task is too big and no job too small for the Sket-Dan.
Both anime have similar humour and great characters. Both both follow and subvert character tropes during their run and both have rather fast paced humour. Albeit Sket dance does have slower moments