The answer depends on your volume and budget tolerance, but here's what most of us are running now:
For high-volume operations, MillionVerifier is still the gold standard for pure verification. They're hitting 98%+ accuracy on deliverability checks and cost about $4 per 1,000 verifications. The API is solid, and they handle enterprise volumes without choking.
Findymail is interesting because it's doing enrichment + verification in one pass. Their verification isn't quite as tight as MillionVerifier, but if you're already using them for finding emails, the combined workflow makes sense. Pricing is higher per verification though.
A lot of teams are running hybrid stacks now. Find emails through Clay's waterfall (Apollo → Hunter → Findymail), then push everything through MillionVerifier for final verification before it hits your sender infrastructure.
The Clay credit economics are brutal if you're doing serious volume. You're paying 3-4x what dedicated verification costs, and their verification quality is inconsistent depending on which provider they route to that day.
One thing to watch: if you're running Smartlead or Instantly, both have native MillionVerifier integrations that can auto-verify during list uploads. Saves you the API work and keeps dirty emails out of your sender pools entirely.
LeadMagic is also worth testing if you want another verification option - they're newer but competitive on accuracy and pricing.