Which reliability measure you are talking about? Write threshold or long term storage?
If it is about how much you can write before the drive is dead, then SSD all the way. In theory, yes HDD has INFINITE ENDURANCE, but the head does get deteriorated overtime, the gas (usually helium) leaking out, heat under load, etc... make it the worst choice for constant data read/write. SSD doesn't have any moving part so it is safe from this.
On the other hand, if you want cold storage (like off-site backup or datahoarding), SSD is a bad choice. Consumer NAND can only store data in power-off state for a minimum 1 year (required by JEDEC standard) in room temp. On the other hand, HDD can store data up to 30-50 years under the same condition. If the condition is optimal, 60-80 years can be reached. So for backup solution, I'd suggest HDD.
TLDR: SSD is reliable under constant read/write, HDD is reliable for off-site storage