Worst: Barely from outer space? Pretty weak punchline in my opinion. Garfield's random change of expression seems out of place too. Shouldn't he be cynical in the last panel instead of shocked? I feel like it would make more sense that way.
Runners-up: Brevity (What does the Energizer Bunny have to do with the Rolling Stones?), Dilbert (Dilbert used to be clever, now it always follows the same set-up: statement, counter-statement, insult), Hagar the Horrible, Mother Goose and Grimm (how many times can you punish a strip for using the same dumb joke? As many times as they use it.), Mutts, Red and Rover, Rhymes with Orange
Best: Lots to love in this one. Poncho's end around attack in panel one. Chazz's misguided decision to take his dog's side instead of his wife's. Carmen's irrational response. His appeal to Poncho for help, and Poncho's completely backwards way of going about it. I enjoyed pretty much everything about this strip. Definitely one of the best to come along in a while.
Runners-up: Agnes, Beetle Bailey, Dennis the Menace, Doonesbury, For Better or For Worse (FBOFW is usually very platitudinous, but sometimes it reaches the level of profound), Get Fuzzy (would of won many days, but Paul Gilligan hit a home run), Pearls Before Swine