There are differing opinions on that. An SSD can offer faster access speed than an HDD. But that is only important where speed is needed. In the audio environment, the HDD provides all the speed that is needed. Having an SSD will not make the B2 boot up any faster (currently ~10 seconds) because the operating system is on the micro SD card.
For me, the important question would be which type would be likely to last longer before a failure. But I don't know the answer to that.
I do know that every disk drive will fail eventually. So it's important to have a backup of all your important data (music).