Screen protectors on all.
iPhone ... Spigen leather Illuzion case, indigo and lemon, which I love because it's beautifully made, lovely colours, perfect fit, easy to use the phone in the case or take it out, and good protection, but it's more like a wallet than a case, I don't want the phone encased i like its design and I like to see it.
iPads .. Just smart covers, blue on ipad2, orange on ipad4.
I suspect that encasing especially the retina iPads might make them run hotter, but I don't know if that's true ... Anyway, I don't care about minor scratching on the back, I do care about protecting the screens. Carry then in slim-fit bags, with pocket on front for the charger and BTkeyboard and a skinny plastic stand fit neatly in the back pocket. Have an Apple BT Keyboard, but usually use the Logitech solar 760 for both iPads and Air, as it has 3 function keys for switching to each. All super portable. The ipads even with keyboard and the stand, carried with shoulder straps, are not heavy.
And a striped satchel for my Air, and pink keyboard cover.
A colour fest!