Suggestions For 5S Cases That Don't Ruin The Looks?

So I've just got my brother a space gray 5S, but as an android user I've no idea what the iPhone case scene is like...except for the fact I know it's far more developed and plentiful than that for android phones.

So firstly I'd like to ask how is the space gray model holding up in general to scratches etc. (I know the old black model had some issues if not looked after carefully), and does it even need a case in your opinion?

As for the cases, can anyone suggest good cases that don't ruin the looks of the phone? Drop impact is not a huge concern, it's more just about keeping it looking nice over the next two years, so ideally something minimal and slim.

As an aside, I know iPhones hold their value really well...but anyone care to guess what a good condition 5S would be worth in the UK in two years time when the 6S is released?