Best iPhone mail app

I have an iPhone 5 and I used Mail for a long time; I had so many problems (emails not viewed correctly, the app is so slow only to send a text email) so I am trying Mailbox and Acompli. I have to manage two accounts, gmail and exchange: Mailbox is fast but I cannot use exchange account and Accompli has still too many bugs. Since I started using this two apps my battery drains more quickly than before and I have to recharge it twice in a day. So I am considering to use Mail again.

Anyone has some suggestions for the best mail app? What do you use?