Personally, original stories.
I have never tried writing fanfictions but even just thinking about it gets my brain knotted. I couldn't precisely nail down the personality of a character I have not personally come up with no matter how much I've read about them but I think fanfictions should stay true to the original in that regard. So, fanfictions are a big no-no for me ability-wise already.
I have actually done translations, albeit of my own stuff (wouldn't do anything else either because it's a difficult thing legality-wise and since I'm living off being an author, I'd rather not get into territory regarding that which could get me in trouble). Let me tell you, it's
effing hard. I actually had some lectures on translating back in university so I had some guidelines on hand for how to go about this, what to take note of etc but actually doing it was still darn frustrating. I can probably churn out a whole story in less time than I need to do a translation of the same story.
Actually, I frickin hate translating my stuff but it actually pays out quite well so the broke artist in me thinks it's still somewhat worth it
Now, original stories are a whole different breed to me. Since I'm making everything up it usually goes fast (since the plotting and world-building and lore-part is actually what I consider myself being best at as an author), I know the characters and how they'll react, I don't even mind missing the mark with phrasing since I know I'll edit it later anyway, and it's just so much more surprising than the translations because I can still discover new aspects I didn't think of before.
So hands-down, I'd always choose writing a completely new, original story over translating an already written one or attempting to write fanfictions.