"I still have doubts."

Translation: Wciąż mam wątpliwości.

[HelbentForleder]

Can it be: Jeszcze mam wątpliwości? And is 'still' really a good word for 'wciąż'? What about 'constantly' or 'continuously'?

[Vengir]

Yes, "still" is a good word for "wciąż" and it fits much better in this question than "constantly/continuously". The more accurate translation for "contantly/continuosly" would be "stale".

[IE99]

Is there a difference between wciąż and jeszcze?

[Vengir]

A little one maybe. „Wciąż” is still in regards of time. As in still meaning now or not yet. „Jeszcze” is more universal. Can't recall at the moment a situation, where you can use „wciąż”, but not „jeszcze”.

[ADJD4]

And so "jeszcze mam wątpliwości" should be accepted here?

[Jellei]

It seems to me slightly different, but yes, acceptable. Added.

"Jeszcze", for me, sounds a bit like "OK, some of my doubts are gone but I have new ones", while "Wciąż" more like "Well, some of my doubts are not gone yet". But this is obviously a subjective opinion.

[JerryMcCarthy99]

A more likely English sentence would be "I still have my doubts".

[Jellei]

It works already. But I rather don't want to risk people trying to write "moje wątpliwości"... whose else doubts one could have, after all.

[BenYoung84]

I think you mean "who else's". As far as I'm aware, "whose else" only means "the other thing of whom".