That's why I chose Oshawott, I think its personality is easily the most annoying of the three. It has this sense of arrogance it never backs up, and it gives up very easily. I think it very well may be the worst battler Ash has ever had (not sure how to compare it with Rowlet since I'm not caught up with original episodes and the series isn't over yet anyway - but I would say worse than Rowlet too) and got as much if not more focus in the series as any other Pokemon, which just led to a lot of annoying, low-quality battles, and it retained its arrogance after losses and poor performances. The whole pop out of the ball on its own to help out in a situation, then decide its too hard and gives up thing was really common and terribly annoying (mildly funny at first, but got old really fast). It was also always at fault with its arguments with Tepig/Pignite yet the blame was typically spread out (I found this rivalry a lot more forced and annoying than Chespin/Pancham - but that may just be personal). The only thing I really liked about Oshawott was when it spiked its shalchop on the ground, then walked over to it slowly to pick it up, because that was pretty funny.
Piplup, I agree I liked it more during re-watches. I think its just because I was prepared for it to be hogging screen time, so I wasn't as disappointed as say I would be waiting weeks to see Pachirisu or Buneary. The personality really wasn't that bad, we just had never had a Pokemon other than Pikachu get that much screen time before so it was something to get used to.