If you said do you trust Microsoft security, who host millions and millions of 365 accounts and I have not heard any major issues, or Readdle/Edison with a limited track record. Who would you choose?
This, of course, opens up the whole can of worms that traditionally plague arguments about which OS is more secure. In that argument, which is a bigger, more rewarding target? A big company who host 'millions and millions' or a smaller company with fewer users? Of course, neither Microsoft nor Apple are small companies (and that also argues for AV software on both platforms) and are open to attack. Or are companies looking for opportunities to monitize our use for their bottom line.
And again, for email, that relies on how comfortable you feel with either (any) company having that data and how 'secure' they actually are.