The first-order classification is whether or not the package has a lid. In general, lidless devices offer better thermal performance due to the fact that they are not adding extra junction-to-case thermal resistance in the form of a TIM1 inside the package between the die and the lid itself. TIM1 is the material applied by AMD within the lidded device package to thermally couple the die to the device lid. Lidless devices allow the thermal solution to get as close as possible to the source of the heat, which is the die. On the other hand, lidded devices can be easier to design with, as they are the more traditional approach to IC packaging, and off-the-shelf thermal solutions can be easier to find. In most basic terms, lidded packages allow the mounting of a flat base thermal solution whereas lidless might require the use of a pedestal milled or otherwise integrated into the thermal solution base to properly contact the die.
From a reliability standpoint, lidded devices do offer more protection to the die while lidless devices with stiffener ring offer higher rigidity. This allows the lidless package to have higher board level reliability (BLR) characteristics. BLR refers to factors that can impact the device adhesion and signal contact to the board such as shock, drop, and vibration. It also can encompass factors like board bend, flex, and deflection that can result in partial or full separation of the device from the board.