They could both be "right", as a person's name and spelling can change during their life, due to error or intentionally. I have several ancestors who changed their own surname spelling during their own lives, and many more who started using different given names at some point.
Very old spellings can vary even within the same document, as not everyone could read and write. Death certificates and gravestones are often "wrong" since they are informed by younger relatives and not the deceased people themselves. Censuses are also often wrong, as the census taker may mishear the interviewee or the information collected may be second-hand from a neighbor or landlord.
To prevent constant changes to profiles as people disagree over the "right" name, WikiTree regard's the chronologically first documented name as the WikiTree name, but then allows alternate names and spellings to be noted in various fields or in the biography itself to clarify further.
In your case you should find the earliest document (of reasonable validity) you can with each of your grandparent's names, use that as the WikiTree name, and add information for variations. If you later find an even earlier valid document with a different spelling, you can update the WikiTree profile accordingly.