Recently, I got an iPad mini 2. Late in the iPad game, but the price was right. I added one e-mail account on the Mail app, and found the swipe right to Mark as (un)read and swipe left to trash to be neat. Except for GMail accounts – when you swipe left, the option is to Archive;
This is inconsistent(especially when you have multiple e-mail accounts and one GMail account!), so this is how I changed the option.
Goto Settings → Mail, Contacts, Calendars → under Accounts → select Gmail → Account → Advanced → under Move Discarded Messages into → select Deleted Mailbox
Afterwards, I noticed that swiping on an GMail item to the left shows;