There are three main types of automatic gearboxes available on modern cars - torque converter automatics, dual-clutch automatics and CVT automatics. All three have their advantages and disadvantages compared to each other, but we would suggest deciding what type of vehicle it is you are looking for and what attributes you need before considering what type of gearbox it has. If reliability is the most important factor then arguably torque converter automatics are the most robust of the three, but once you have narrowed down your vehicle choices you can look for any specific reliability issues.