i prefer the GMail app vs the Stock app b/c i've multiple replies to single emails--"threads" and the Stock app will display each one as a single email, whereas Gmail app will only show one email.
so instead of scrolling through 45 emails (duplicates of a single email with one new line response), the Gmail app will show you the email itself, and upon tapping it--will take you to the newest response.
it just looks cleaner to me. but, to each his/her own
(yes, Stock app enables Conversation view by scrolling along the bottom icons--but i prefer this to be default, which can't be done on the Stock app)