KR cases are both cheaper (from memory) and nicer than GW ones
If you're going to be taking the models far/on public transport/out in the wet the aluminium ones are very good, otherwise the card ones are good.
What you might want to do is use the "choose by army" option on the KR site to make sure you get the foam with the right size slots, as for example Kroot need a slightly bigger slot than FireWarriors (largely because the kroot have bigger guns, and are slightly taller).
I've been using the KR cases practically since they first started and remain very impressed with them, especially now they do the precut custom foam (a godsend for things like tanks, fighters/bombers etc).
I think they've started (or should be soon, I gave up waiting) doing a selection tool that lets you enter in what your army has and it suggests tray sets to get the most efficient storage.
One suggestion though, once you get more than a couple of KR cases it's worth putting something on them to let you remember what's in them easily - I've put labels on the card cases that I intend to permanently store my Tau on for example (I'm up to about 7 card cases and it's annoying having to hunt for the right one).