I'm not using a case as such of the majority of the time. As with all of my devices I just use a clear skin on the back. It keeps the looks, stops it getting scratched and adds no discernible weight or bulk. And a screen protector on the front, for obvious reasons.
But I do have the Smart Keyboard which doesn't always get used and I have a nice leather case for the very rare occasions when I know I'll be needing a bit of added protection. I've also got a Moko case that I got as a stand-in, but that doesn't get used any more (If anyone wants it, (in the UK) give me a shout and you can have it, gratis of course, I don't need it. It's been used less than two days and hasn't left the house, here's a piccie)
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But for the vast majority of the time it's just the skin and tempered glass screen protector combo in use and after only a few hours I don't even feel the difference in weight it's so minimal. But the Pro is nice and protected from all but a big old drop, but that's what I've got AppleCare+ for