Which Mobile-app Framework is ‘Best’?

I’m trying to develop a cross-platform, social-media mobile app that relies heavily on location-data and map-API integration. I have some experience with software engineering but almost none with mobile development. I’ve tried several frameworks over the last couple weeks, and my favorites are React Native and Flutter.

So, of those two frameworks, does either have any major advantage? The most important attributes to me are (A) high security of the data flowing between stacks, (B) clean separation between these stacks (i.e., separation of interests), and (C) a simplistic method of transferring data between stacks.

It seems to me that Flutter covers A and C better while React Native separates the front- and back- end a bit more. Is that correct? If so, is the difference significant? More than anything, I’m worried about privacy/security; that is I don’t want to use metaphorical GET calls if POST calls are available elsewhere. Thanks in advance for the help, I really appreciate it!