While ball bearings have some key benefits over sleeve bearings, esp. when horizontal, the various flavors of fluid dynamic bearings are usually even better. Ball bearings are long lasting and don't have the directional lubrication issues of sleeve bearings, but they can often end up noisier because they're very easily damaged in shipping. Just drop the package on the floor once, and you can end up with micro-dents in the bearing ring surface that cause clicking or buzzing forever.
Fluid dynamic bearings are great because they minimize any sort of metal-on-metal contact, and float the fan axle in the middle of a spinning sheath of oil. That makes them very quiet, and also very durable since there's little wear. Since fluid bearings are generally considered better, there are also many more fans available that use them. The tech goes by various names as each company tries to put their own proprietary touches on it; Noctua has "SSO2" (self-stabilizing oil pressure), Thermalright has "Enhanced Hyper-flow", etc., plus there's lots of variations on "fluid", "hydraulic", "flux" etc.
You don't mention whether you're looking for PWM or solely voltage-controlled fans, or just planning on running them at full 12 volt max all the time; that makes a big difference for suggestions.
If you decide to go for fluid bearing fans, the Noctua series is very high quality and hard to beat; I have NF-A15 PWM fans and love them. Thermalright TY-140 or TY-147 are also very good, as is the Corsair AF140 Quiet Edition. If you stick to ball bearing, then Thermalright TY-141 is probably about the best, and the Prolimatech Ultra Sleek Vortex 14 is also very good (but thin, which can be good or bad).