1: Either Rainbowdash or Fluttershy
Sexual connotations aside, RD is entertaining mainly in her often complete abandonment when it comes to the consequences of her actions and thus charges blindly into anything, often resulting in a pretty entertaining outcome.
On the other hand, Fluttershy is essentially the opposite as she'd rather not rush into any situation, and is reluctant to do anything - the result though of what happens when she does actually do something is always really unexpected since it's so deeply in contradiction to the rest of her character - essentially the main humor from her comes from juxtaposition.
2: Pinky-pie or Twilight
Essentially dealing with opposites again, ADD is often quite humorous, which PP is essentially the embodiment of - she's like the summation of popular youtube videos into one random, non-sequitor happening.
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