I also do a single panel. Some people like it some don't (which sums up everyone's experience, I guess). Single panels sometimes get dismissed as "gag a day" comics, which some definitely are, but the promise for the single panel goes much further. The relatively unknown B. Kliban, for example, did amazing things with single panels. The problem with the format is that people have come to expect instantly comprehensible jokes when seeing one 1 frame. In short, they have come to expect - self-fulfilling prophecy - gags. Working against those expectations while trying to do something more interesting with the medium remains one of its greatest challenges.