Hiya creepily requires access to all of my contacts, which I think they transmit to their servers for vaguely specified reasons.
Truecaller creepily requires my name, phone number, and email address to add to their directory, which I think might allow people to find my phone number under vaguely specified conditions.
I had Hiya installed for weeks and it never identified a single spam call, during which time I got about ten. I followed all of their voodoo troubleshooting steps, but it just never worked, so I deleted it. (Too bad I can’t un-send them my contacts. Thanks a lot.)
I’ve had Truecaller installed for a few days and it has already correctly identified two spam calls with no drama or voodoo required. It just works.
Update: Readers told me about Nomorobo, which appears to both work and not be creepy. The best of both worlds!