If you care about the opinion of someone whose absolute favorite hero is Slark, I can tell you that he feels very smooth to play, and going around in the enemy jungle to pick off farming cores and supports feels very satisfying. You get to roam around and kill people before other carries do, while also retaining the ability to farm waves and camps fast. If you're decent at the hero, you rarely ever fall behind once you get beyond the first few levels, which truly are his only weakpoint (even though you can cheese people level 2 with some supports), you're likely the one with the highest chance to snowball simply because you're playing Slark, and almost every game you get to do stuff while many other carries sit back and farm.

Now, I am a trash tier player, but I think what I wrote is pretty reasonable. I also don't spam Slark, it's just the hero I play the most. To put it in another way, I don't get tired of playing Slark, it's just that there are other heroes worth playing as well. Why wouldn't I rather play Puck or QoP? I don't know, they just never clicked with me. Why wouldn't I rather play ES? Which one though? However I like playing them all, I dunno maybe it's relevant for some statistical purposes.

Also fish memes, there's that also. Undeniably.