OneDrive,
in that it presumes the internet is perfect and mobile phone data connections never break.
In consequence, when I used iCloud to put an important document on my phone,
then went to check the document when I was in an area with poor mobile connectively,
I found that iCloud had lost the document. Since the document contained an address and a map, this was extremely irritating.
OneDrive has the same bug. Fortunately for me, I’d learnt my lesson from the OneDrive bug, and saved a copy of the document elsewhere.
I can recommend neither OneDrive or iCloud for cloud activities on a phone, they both contain nasty bugs that make the products pretty unreliable.
Still, if I have to suggest one, I’d suggest OneDrive: it’s actually usable.
Which phone is better: well, ironically, it’s a much of a muchness because Microsoft is on both phones.