Why are these my favorite shows? The same reason I love any show. They aren't very serious; the writing is fantastic. The actors were perfectly cast. Honestly, Sheldon Cooper and Penny on Big Bang Theory and Chuck Bartowski, John Casey (Adam Baldwin, of Firefly and Serenity fame), and Morgan Grimes are some of the best characters on TV right now. Sadly, Chuck and The Big Bang Theory run opposite each other on Monday; the former being an hour-long show starting at 8, and the latter a half-hour show starting at the same time. If you must only choose one, pick Chuck, which has better characters and production quality and boasts a more promising storyline; but full episodes of Chuck are available on www.nbc.com, whereas the episodes of The Big Bang Theory can only be found, ahem, subversively.
Yes, I hear what you're saying...good shows only ever get cancelled by FOX! (*sigh* Firefly, Arrested Development....tragedies...) But with Pushing Daisies and some others, there is now precedent for even non-FOX networks' cancelling shows with small but loyal followings. Give these shows a try!
WATCH! Chuck episodes, webisodes, and episode re-caps can be found here, for those wishing to catch up on the action; CBS's much poorer Big Bang website, sans full episodes, can be found here.