It depends on your priorities, really. CVT gearboxes aren't as refined but are generally reliable. Dual-clutch gearboxes are more complicated so can go expensively wrong, but also provide very quick, smooth responses and good fuel economy. Traditional torque-converter gearboxes are usually less efficient and a little slower to respond but can be very robust. Automated manuals aren't very smooth or quick to respond but are cheap to produce, so are popular in small cars where cost is key.