Between the two, sanded grout is normally the choice of a lot of people when they would like to do some flooring installations. The main reason for this is durability. Between the two, sanded grout is considered to be more stable and sturdier as compared to unsanded grout.
If you are going to make use of large joints, sanded grout can be the better option but if you are only working on small projects, there is nothing wrong with using unsanded grouts. Just make sure that you are going to use it in a place wherein you know that there will not be a lot of foot traffic. Unsanded grout may not be able to take too much foot traffic.