Feel + firmness
Winner: Saatva ClassicThese are not two versions of the same bed. The Casper Original Hybrid is a foam-led build — AirScape breathable foam over pocketed coils, 11″ tall, one firmness only at 6/10 medium, with zoned support that firms under the hips and softens under the shoulders. You get contour first and bounce second. The Saatva Classic is a dual-coil innerspring at 11.5″ or 14.5″, sold in three firmness levels — 3/10 plush soft, 6/10 luxury firm, 8/10 firm — where you get support and lift first and contour second.
The decisive difference is that Saatva lets you choose and Casper does not. Casper's 6/10 is the safe middle, and for a lot of sleepers the safe middle is exactly right. But if you're a stomach sleeper who needs the hips held up, or a strict side sleeper who wants to sink, Casper has no other build to offer you and Saatva has one waiting. Saatva's own guidance puts roughly 85% of buyers on the Luxury Firm 6/10, which lands in the same neighbourhood as Casper's single option — so for the typical buyer these two beds compete directly, and the choice comes down to whether you'd rather be cradled or supported.
Worth saying plainly: firmness is a preference, not a quality score, and neither of us has slept on your body. The published literature is only mildly helpful here — the review Saatva's page cites (Caggiari et al., Journal of Orthopaedics and Traumatology, 2021) concludes that medium-firm surfaces tend to suit most people for back pain and sleep quality, which is a description of both of these beds rather than a tiebreak between them.

