(I am biased tword H-drives, to take my two cents with two cents-worth of salt)
I think both H-drives and X-drives will be great for this game. Since you would need to use many half-motors for a 6m X-drive. I think H-drives will work well this year. Also, if you are using a change-up style robo like @9motorgang’s robot, you could fit a PTO in there and still have pleny of space for the blocks. If you are planning an a 4m drive, x-drives will be easier, but a 4m H-drive would let you designate a motor for the H-drive.
If you do use an H-drive, I would do it like this:
1417R RachmaniBOTS Robot Reveal scoll down to the H-drive section.
If you have any questions on the “Deca-drive” please let me know and I will share what I know.