TV land recently ran a marathon of old Dick Van Dyke shows which are celebrating their 50th anniversary. I know this isn't a current sitcom but it was one of the first great ones. Everything in this show just "worked'. The characters were great and the writing was terrific.
I have to say, honestly, that I don't watch any current batch of sitcoms on the air right now but I really love the old ones from the 60's.