Never seen modern family, so couldn't tell you.
I only saw a few episodes of How I Met Your Mother, and the first few times I could see it being okay (especially since it had my favorite actress from the Buffy/American Pie series) but after a while I started to really desire a root canal rather than watching the show.
Only saw Two and a Half Men when Sheen was on there, and stopped watching before Ashton Kutcher, so I'm not really able to say whether I like it or not, although I thought that when Sheen was in there the show was hilarious.
Big Bang Theory... two words... CANCEL NOW! I have seriously never found that show funny in the slightest, and actually felt every reason to just turn off the television... which I've done to the point where I don't watch anything on television anymore.
All of those pale in comparison to (in my opinion) as the worst show on television. The thing has no comedic value, absolutely no viable story, hardly any decent talent, and even less reason to bring that talent onto my screen. I am, of course, referencing The Office, and figure that the only reason why it's even on is because people are waiting for something better to come on and don't want to turn off the television for fear of losing track of time and missing the show they really want to see.
Mind you, this is my opinion, and if you have something different, then I'll respect it, but seriously I don't see why the last two shows I've mentioned are even still on the television at this time.