If you want to make a precise machine that doesn't need a lot of maintenance then belts are a must. In my book, there are two reasons to use fishing line. It is cheaper. It can do routings that belts can't. I would put precision of both belts and strings at about the same level. However, string creep and tension will change more between prints than a belt will.
For you I would say it was a decision between cheap or worry free.
For you I would say it was a decision between cheap or worry free.