The types refer to the shape (the squares and circles) on your GPU connector: https://graphicscardhub.com/graphics-card-pcie-power-connectors/
I would recommend buying both types to see which fits and be able to use them for any future GPUs.
Couple more questions:
How many ports does the distro have? I’m thinking that I could attach a temperature sensor to the bottom port.
Additionally, where would be the best place to mount an Aquacomputer Quadro?