at this point, there is very little chance that IC trucks will be the correct choice, newer (A/C controllers) electrics will have the lowest long term cost of ownership.
The only way an I/C truck can long term be more cost effective is in larger size units and/or rough terrain or on non-improved surfaces.
you might try "lift-truck-cost-tool dot com" a site Jungheinrich has set up to help make this argument.

But we need to choose only one type because of the initial costs of the stations.
I need to find some studies or some document that includes the advantages and disadvantages of electric and gas forklifts.
I have until the end of the week to decide.

Hello Cavalinhos
You need to find a reliable experienced adviser to help with this decision. It is not a straight forward choice but an informed opinion based on the working conditions and use. The right choice could be either, or more likely a mixture depending on you individual requirements.