Ondansetron or Meclizine?

So, after reading comments here, what has everyone had better results NOT vomiting with while doing prep: ondansetron or meclizine (Bonine)? I hear ondansetron can draw water out of your body, thus causing constipation. My GI did give it to me, but I'm worried it will interrupt what the prep might do?

I regularly take meclizine but feel like that might not help this type of nausea, however.

I'd rather take the ondansetron, tbh, but don't want the prep to get interrupted.