I use Silverstone 12cm fans and they work fantastic, rifle bearings so they can be mounted in any position w/o too much linear movement.
What you want to look for in a good fan is the bearings, airflow/blade design, and how you want to plug it in.
I recommend, hydrodynamic bearing, rifle, and ball bearing fans. They are usually a little pricier than the base model sleeve bearing but they will pay you back in longevity and peaceful quiet.
IDK about 8cm fans... however for your 14cm solution, I would either get a 14cm fan that can keep up w/ all the other fans, or, get a 12cm fan to keep positive pressure in the case to slow down how much dust accumulates.
Hope this helps.