The most reliable 90's game are Gottlieb System 3 machines. They are rock solid but apart from Stargate and Freddy's Nightmare, they are not players. Data East are VERY reliable machines if reconditioned properly. Late Sterns are also reliable. Bally / Williams are the least reliable, and the most collectible.

As with any purchase, if they are in good condition and reconditioned or restored properly, they will be reliable - regardless of manufacturer. But as all games have "moving parts", they can develop issues.