I don't think Tribbles had the funniest scenes, but the whole episode was just so light hearted... even with the Klingons around, you didn't get any sensation of real concern from the crew. So, there's all the ridiculous fuzz balls all over everywhere, with some people overtly fauning over them (like Uhura). Then you have Cyrano, the peddler. In retrospect, I'd say that "I, Mudd" was probably a little funnier.
By Any Other Name certainly starts out very serious... the crew is totally whipped, no question about it. You start wondering "well, I know this is a series, so there has got to be an ending to this somehow where they all escape..." and then the tide turns, it all becomes very light hearted and funny, especially the scene with Scotty and the Kelvan totally smashed.
Eden was still pretty serious, in my book, despite the cartoonish garb of the space hippies. But I never found myself laughing at any point through it. Only the occasional smirk, like at Adam with his "that's like NOW" and "I'll spread the word" as he captures air with his hands. The concept was pretty cool... very smart young people who have a radical agenda to completely escape from the modern world
... I also like how much it mirrored the social strife of the younger generation of the time that was just about cooling off (the end of the turbulent 60's, 'Eden' aired in February 1969).