Nectar: 365-night trial (industry-leading), Forever Warranty. Casper: 100-night trial, 10-year warranty. A year to decide is enough to know whether a mattress is right; 100 nights can expire before the season that exposes the problem.
Availability is now the bigger gap, and it is worth being blunt about it. Casper has discontinued the Original Hybrid — casper.com/mattresses/casper-original-hybrid redirects to the Casper Dream Hybrid, a different bed at a different height and price, and Casper's own upgrade guidance points Original owners at the Dream. What is left is Amazon stock under ASIN B085H9FBBP at $1,495, listed as limited quantity. Nectar Premier is still in production and sold direct at $999.
That matters beyond ordering. Warranty and trial claims on a discontinued line are only as good as the seller behind them, and if the bed doesn't work out there is no brand-direct replacement unit to exchange into. If you want the Casper feel from a bed that is still made, the Dream Hybrid is the model to look at instead.