mecanum drive is probably easier to build, but as far as I’m aware the code is exactly the same as with an x drive.
One thing you should ask yourself (which you may have already done) before making a choice between x and mecanum drive is if you are confident that you will be able to make good use of a holonomic drive. I see a lot of teams make x or mecanum drives because in theory they are better (why wouldn’t you want to move in all directions?) but in practice the added complexity and tradeoffs make it only better than tank drives when used well. That said, the best way to find out if you can make good use of a holonomic drive is to try one, and don’t let me discourage you from doing that if your intent is to learn and experiment.
If you’re still stuck on the decision between x and mecanum drives, see this topic, there is some good discussion about the pros and cons of each: