Still haven't decided on a robot
If the robot chosen is designed in a sufficiently modular way, maybe it would be good to have simpler variants of the robot used in early sections to explain things, while keeping the same robot framework used in the late sections.
As far as which robot, I haven't been browsing the code of many robots lately but I feel like Diamond is one of the more cleanly designed ones for the most part, however for the purposes of this type of guide has the drawback of having a lot of melee-related code. DrussGT is well-coded, though the way in which it is (last I checked) less modular than some others may make it not as easy to organize how it's explained in the guide. I haven't yet looked at Gilgalad and XanderCat and some others though I think I will take a look shortly out of curiousity in any case. In any case though, I think the most important thing for the choice of robot is how clearly the one writing the guide understands it :)