Why do you think species have evolved to use ATP rather than GTP?

First of all, the difference between them is that ATP contains the base adenosine and GTP contains guanosine. One of the significant differences between these molecules is that guanosine contains an extra oxygen atom. This may have acted as a selective disadvantages as species were evolving in an atmosphere with a lower oxygen content. Consequently, by the process of natural selection, species with ATP evolved.