Easier to code? The drive code has always been the same for both in my experience.
I think x is better as there is more mobility (diagonals for auton) and it is faster than a mecanum drive. This game is about speed, and since the field is pretty much open speeding across is going to be a necessity.
I think that one thing that people overlook with mecanums in terms of speed is that their higher torque should result in better acceleration. Also, mecanum drives can be easily geared up to around the same speeds as an X-drive while maintaining higher torque, whereas x-drive gearing while possible is more difficult and bulky and sacrifices even more torque to which is already lacking. For example, a 4 inch 200 rpm Omni x drive is about as fast in the axial direction as a 280 RPM mec drive.
If you gear the mecanum to the same speed of the X drive, then you lose torque.
Why would you need to use a gear train on an x drive?