About rooting in water, there are advantages and disadvantages. The good thing about water rooting is that you can see the roots develop. However, with a plant this easy to root, it is not really important. If you do root in water my advice would be to switch them to your growing medium as some as the root nodes develop. It is best to do this because plants form a different type of root in water than they do in soil. (Yes, they do!) With a plant this easy it really doesn't make any real difference, but with many plants the difference is significant. Water roots are very fleshy and very fragile. They tend to bruise or break very easily. When a plant has a lot of water roots many of them die in soil as new roots are formed. Finale word of caution; if you use a mix, best to use a sterile mix and if you use water, change the water at least every third day and better yet, every day. But if you are curious, try different methods. I continually experiment and I have been rooting plants on and off for over 50 years. There are a lot of tips you can garner from other people who propagate by cuttings. One example is additives of other ingredients. These are very broad in scope and many of them work quite well. Things like willow water, aspirin, hydrogen peroxide, b- vitamins ... and the list goes on. None of these are really important with willow ficus because they are so easy, but it is fun to experiment.
Wish you the best, but whatever method you use you are quite likely to have some success.