which are the Intel Nuc Kit without fan? Can all of them be equipped with an ssd? Which do you think is the best?
There are no NUCs that come fanless.
You can purchase after-market fanless chassis and move a NUC board into it, however. All of the NUCs supported can utilize a M.2 NVMe/SATA SSD. Some chassis also support a drive bay for a 2.5" SATA HDD/SSHD/SSD.
To get an idea on which NUCs are supported, by what manufacturer and where you can purchase them, do an internet search using "fanless chassis for nuc".
Hope this helps,