Using mailbox app, since I had my gmail account long before I got my iphone, and my workplace uses gmail for their mail as well. No reason to switch to icloud personally.
The gmail app for IOS sucks (IMO) since it still lacks a unified inbox and can't open attachments in apps. Jumped into the mailbox app when it was released (waited roughly a month for it) and liked its swipe features enough to tolerate its shortcomings for now (lack of landscape mode, doesn't pre-download mail).
Will probably stick with mailbox, since I intend to recontract to a 5s (or whatever Apple calls their iphone for this year), and have heard that Google no longer supports push email for the iphone.