Depends on what you're doing, I have 3. SSD for startup, 1TB HDD for 'home/admin' and 2TB HDD for railway pics and vids (and 2 more 2TB externals to back everything up).
Agree with Metr0land, don't rely on SSD as primary storage without backing up. We have fitted SSDs from a number of manufacturers and all of them have died within 2 years - and once they die you can't recover data from them, unlike spinning disks.
