I'd argue that if you ever end up paging out to disk, regardless of where that disk is (e.g. HDD, SSD), you should probably consider adding more RAM to the system. Although SSDs are significantly faster than HDDs, especially for random seeking, SSDs still have 10-100x less throughput and response time than the equivalent RAM would.
If you end up paging out to disk, to either an HDD or SSD, your computer will become unbearably slow.
For that reason, I personally would (and do) put the pagefile on the HDD, since SSDs have a limited number of writes. Having a pagefile on the SSD would only cause the drive to wear out faster (assuming you're even using your pagefile to begin with).
TL,DR: If you're paging, your system is going to be very very slow, regardless of wether or not the pagefile is on an SSD or HDD, since both are many orders of magnitude slower than RAM is to begin with. Given that point, I would place the pagefile on the HDD, since SSDs have limited numbers of writes.