I used the 400r for awhile but changed to the HAF 932 advanced.
It all depends on what you need. Don't underestimate the importance of the case.
I for one wanted to do water cooling, push/pull, then found that 400r couldn't do that.
But if you don't think you'll ever want to do that then the 400R is a decent case.
But if it's possible, go for the 500R. The extra options it has makes it worth it in my opinion.
I only didn't go for the 500R in the first place was that I didn't know about it.... Still would of liked more room anyhow.
Corsair's cases are all nice, it just depends on what you need/are willing to pay for.
800D is pretty cheap (compared to it's usual $300 price) @ Newegg.com right now if you want something with plenty of options.