Engineered quartz is roughly 90-95% ground natural quartz mineral bound with polyester resin under pressure — factory-made, not quarried. Because the resin binder is not heat-stable, it is not marketed as an outdoor or high-heat surface.
Sintered stone is produced by compressing mineral powders (often similar to those in porcelain) under extreme heat and pressure with no resin binder, producing a very hard, low-porosity slab marketed as more heat- and UV-resistant than resin-bound quartz.
Solid surface is an acrylic or polyester-based material, filled with mineral powder, that can be thermoformed and seamlessly joined — useful for integrated sinks and curved forms that slab materials cannot achieve.
Why manufacturers built these categories
Each was developed to solve a specific limitation of natural stone: engineered quartz addressed the need for a low-maintenance, non-porous countertop that never needs sealing. Sintered stone targeted the heat- and UV-sensitivity of resin-bound quartz for outdoor and high-heat kitchen use. Solid surface solved seamless integration and repairability, since scratches can often be sanded out rather than requiring replacement.
None of them are inherently "better" than natural stone — they are different trade-offs, and the right choice depends on which limitation of natural stone actually matters for your project.