If you can I'd go bigger diameter and keep them plain. I've had grooved and they send a lot of vibration/judder, it's a hard feeling to describe, back through the brake pedal. The cross drilled aren't so bad for the vibration but as mentioned are prone to cracking. My cross drilled allowed for rust scale/metal flaking at the back of the disc around one of the holes and caused a slight rippling on the disc surface which can be felt through the pedal under heavy braking. It'll need changed shortly.