Native Samsung Email app?

I don't think its any better than Outlook, or Gmail. I personally use Gmail for everything. I love it. Sync's beautifully, and it just works.
 
Now that GMail supports Exchange Server (it didn't used to), there's no reason to use Outlook. (It's not like Desktop Outlook - it doesn't sync to the rest of an Office system.)

Since Samsung removed the checkboxes from the left column, I stopped using it - that was the only thing about it that I liked. After about a year of trying everything else, I went back to Gmail.

The only difference these days is the user interface, so use the one you're most comfortable with. They all work the same under the hood now.