OK, well I'm extrapolating this from my experience with two kids. It seems like one is often cruising happily along while the other is a struggle. Same with triathlon sports. It seems I always have one favorite, but that position rotates pretty regularly among the three sports. Conversely one is often annoying.
Right now swimming has me jazzed, and I'm not sure why, but I'm going with it. Running has me annoyed, primarily because I've got some off-again on-again foot pain that is distracting.