Actually, with the exception of the Jay Leno tickets picked up from inside the Universal Studios park, most TV show tickets you see people giving out will be standby tickets. They typically give out 25-50% more tickets than they have seats, so you may have to show up 3 hours early to ensure that you get in.
That said, if you are planning to go to Universal, I would recommend the Jay Leno tickets. Only the ones from inside the park will be guarenteed (not the ones offered at CityWalk). You can tell because the word "GUARENTEED" will be stamped on them. Leno is a fun show to watch live, and unlike many sitcoms you won't be sitting there for hours (most sitcom tapings can take 3 or 4 hours, and much of that time will be spent listening to an MC try to fill the time during costume and set changes).
If you really want to see a sitcom tape, Paramount does offer a very limited number of guarenteed tickets to the shows they tape. To reserve tickets, you have to call (323) 956-1777 at 9 a.m. exactly five days in before the taping date (reserved tickets are often gone in minutes). Once you have a reservation, you must call back to confirm between 9-11 AM on the day of the show or you'll lose your seats.