Going by this there are varying flow rates and pressures for each -->
https://www.merlinmotorsport.co.uk/...l-pumps-for-vehicles-running-carburettors-282
The square ones don't have as much 'lift' as the cylinder ones and need to be mounted near the tank.
The Posi-flow ones a new version of the square ones and are quieter and have a good 'lift' as well as a check valve to prevent fuel draining back.
The cylinder ones have a replaceable filter and magnet to collect particles. You also have a much wider range of unions and can be mounted anywhere. The top spec one has the highest flow rate of all.
Here's a more readable guide for the PSI and flow rates -->
https://www.flexolite.co.uk/images/ul/Fuel systems components.pdf