This is personal preference to be honest. We recommend igus® bearings as they are lightweigh, hard wearing, can have their service life calculated and are lubrication-free
Depending on the bearing depends on how easy or difficult it is to replace. If they are igus® plain bearings they should be easy to replace.
Again, as above, it is dependent on the bearing. igus® bearings tend to be able to match metallic bearings like for like so if you are changing a metallic bearing on a scooter, you may want to consider changing it to an igus® plain bearing