feh...ppl get carried away with too many lights...tacky! Yes 98% of you!
That said...look for the decibal rating, rotations per minute and airflow...many times with that pattern in that order. Airflow will be cfm, cubic feet per minute.
If you'll join the overclocking union, focus on rpm.
If you're like me, and don't ever plan to overclock look for db level. I picked a perfect case with 1 fan, ordered 2 and will order 1 more. 1 front, 1 back and 2 from the side. The side ones I will most likely have one suck out and one push in...but I'll see on that
If you want to have more fun and are an over clocker, get high rpm, mid-high range db ratings and purchase dampening kits to dampen your case.
Helpful Tip: buying large fans can allow you to look for lower rotation speeds that move adequate air and have lower db.
Then for eye candy, you can look for lights, uv reactive materials, both in the fan construct as well as cabling.