There is probably no much difference between the two.
The reason I have tried with 3.0.2 is that the minimun required RAM for installation is 4G.
With 3.1.1 it is 6 G, and I have a limitation in memory.
Or does someone know if it possible to perform the installation with less RAM that what is specified?
I was working in a multi-virtual-servers environments and had probably a problem with not enough memory while installing.
I increased the size of the dedicated instance for the repository (although I am not really sure this was the problem).
I could perform the installation with 1G for the dedicated database and 3 G for the VM Manager.