It's not Mr. Mxyzptlk, which that same Countdown to Final Crisis identified with the Trickster God outright. I haven't read many Superman stories but I plan to dip my toe in the Silver Age shortly, so who knows, the Imp From the 5th Dimension may well take the honors next year.
But the Trickster I celebrate this year is that red-headed rascal, that boater-hatted be-bowtied Beau Brummel, History's Least Efficient Assassin,
Platform shoes and a white tuxedo. Consider that a shopping list.