Airflow is important, but then making sure dust doesn't build up too much can be just as important.
If you go for one of these sound proofed cases you tend to find they take less fans because the idea is you only really want an intake at the front and ejector out the back. This usually means less dust though and even more so if you have a filter on your intake (just remember to clean this regularly). So you wont have too many side fans, underside fans, roof fans etc.
But then you can go for a case which offers all of those and you'll find your case is pretty cool. For instance my Z9 has an intake apache at the front, an intake akasa on the side and an apache pushing air out over my H50 out the back and another akasa pulling air in from the top. My case temps inside tend to range from about 19 degrees up to about 28 depending on what I'm doing.
All depends on the individual and what you want really. Remember these components can get fairly warm and are perfectly stable, but that does mean your room can get incredibly hot!
Important pointers to help with your airflow would be to get some good quality fans if you're not using too many. Such as the Akasa Apache Black, the Noctua NF-P12 or Scythe Gentle typhoon but to name a few. Also make sure your cable management is up to scratch. Braid them cables if you can and try to use your cable routes as well as possible.
Also remember the more HDD's, graphics card etc you have the more heat that will be generated. If you can, try and have perhaps a 1GB green storage drive and say a 120GB SSD (this is a preference but obviously costs a fair bit). For the best air flow you'll want either a midi tower case or a full size case, but which to get depends also entirely on your budget.