Out of curiousity, can I ask why? It seems odd when both support multiple accounts.
Nine I use for work. Everything else is AquaMail. Nine allows me to touch a sender and see there office 365 account info but AquaMail doesn't and gives the excuse they can't. I am tech support for 4 sites and this info is used to no which site an email is coming from when the user fails to tell you or isn't in there signature.
They both handle multiple accounts but AquaMail support backing up both settings and the accounts and Nine only backs up the settings. AquaMail search is also quicker and can search inside an open email. AquaMail also receives more frequent updates.
