From what I have seen in iGaming, I would put SOFTSWISS, EveryMatrix, Slotegrator, and Playage Gaming on a serious shortlist.
SOFTSWISS has been around for years and has a mature casino platform with a large game ecosystem. EveryMatrix is strong for larger operators that want casino, sportsbook, and modular technology in one setup. Playage Gaming is newer compared with those names, but it is interesting because it combines games, payments, CRM, backend tools, affiliate management, and other operator tools inside one platform.
I would not trust any provider just because the brand is popular, though. I normally look at how stable the platform is, how quickly support responds, how much control the operator gets, whether player data can be migrated, and how easily new payments, games, or tools can be added later.
A good sales demo is easy to make. The real test is how the platform performs six months after launch when your operations team is using it every day.