There are two primary types of drillpresses in the market today: benchtop and open frame floor mount models. Floor mount models offer larger capcaity. Benchtop models are easy to move and integrate into a shop.
The quality of the motor assembly mounted on the stand determines most of the other properties of the drillpress.
The shape and features of the table do add utility to the drillpress. Supports for long workpieces are a useful feature. It is, however, common practice amongst woodworkers to build a custom table for the drillpress, which renders most table features a moot point.
The most important consideration when buying a drillpress is choosing the correct size. Swing, height, and plunge limit the maximum size of the workpiece you can drill into. If the drillpress is too small, the workpiece will hit the column, the floor, or the drillbit and cannot be positioned properly.
Higher quality models use higher quality compents. These machines will have higher service life, fewer vibrations during use, and better ergonomics.
If you require frequent speed changes, consider gearhead models. While considerably more expensive, speed changes can be done in seconds on these models.