Travelling by train, you will not be able to see the awesome landscape as if you would on a bus. The rails are in the lower levels, thus your view is blocked by the surrounding mountains.

There is only one early train at 6:25 in the morning and returns at 5:55. It takes about 2.30 to 3 hours to get to Mostar. A roundtrip ticket costs 16KM, which is cheaper than a bus ticket. There are many busses departing to Mostart starting around 7 a.m.

If you go to Mostar for only one day, then take the earliest train or bus you can. The first time I went to Mostar, it was a whimsical decision without planning. The bus arrived Mostar at at 2 p.m. and I had to leave at 6 because it is the last bus belong to the company from which I bought my ticket). The guy whom I met on the bus got to stay longer since he bought a one-way ticket and could choose whenever to leave from Mostar.