Big Bang Theory cons:

• Scenes in later seasons are given no time to breathe or develop. Many scenes are created for a singular joke, but cut to the B plot before we can see the aftermath or reactions. Scenes in Big Bang Theory were just so short

• Midway through its run, the show stops being about nerds doing nerdy things and almost completely begins to focus on relationship drama exclusively

 

Modern Family cons:

• Almost all the Mitch/Cam plotlines are built on dishonesty. They constantly don't want to tell each other something, which leads to farce.

• All the kid actors aged out of their cute, quirky personalities. Manny was an "old soul" in a little kid's body. However, when he was high school/college age, the schtick was insufferable. For Luke, it stopped being "dumb kid" and became "mentally disabled adult"

• Haley and Alex's characters graduated High School, so the show struggled to find reasons to keep them in the house and with the family

 

Overall, I would say that Modern Family's characters were more endearing and their comedic plotlines more consistent than Big Bang Theory.