There are really only two basic types of solar pumps; positive displacement and centrifugal and these can both be subdivided into surface mount and submersible categories. Your water source will dictate whether you need to use a surface mount or submersible pump while your daily volume requirement and total dynamic head (TDH) will determine if you need a positive displacement pump or centrifugal pump.
In general, positive displacement pumps (diaphragm, piston, helical rotor, etc.) are best used where the TDH is high and the daily volume requirement is low. Positive displacement pumps usually require less power to operate than a centrifugal pump and they will produce some water even in cloudy conditions where a centrifugal pump might not. Centrifugal pumps are good in situations where the TDH is low and the daily volume requirement is high.
One of the disadvantages of a centrifugal pump is that it has to operate at a high enough rpm to push the water all the way out of the well. If it is cloudy and the solar array is not producing enough power, the pump/motor may be turning but not fast enough to do this.
Using a tracker is highly recommended with a centrifugal pump since it increases the solar array's power output over a longer period of time which increases your daily volume of water delivered.