Torque. The torque you’re going to be able to extract from your board is correlated directly to your maximum current output. It is important to note that if you are going to use a HyperCore, this motor saturates at about 120 amps, meaning any additional current is just turned into heat and wasted.
Speed. Speed is a 1 to 1 ratio to voltage. If at 15s you can ride 15mph then at 20s you will be able to go 20 mph. Any pack rated at 17s or higher provides ample headroom for speeds exceeding 30 mph, especially with field weakening in play. So this really only matters if you want decent torque at higher speeds. (see field weakening for more info)
Cooling. Heat is proportional to your current. If you plan to push more amps you should plan to be able to cool more. Considerations should include the type of enclosure used—whether it's fully 3D printed or constructed from aluminum—and other relevant factors.
Size. Ensuring your chosen controller fits within your enclosure is crucial. For instance, the Tronic 250r, being taller than alternative controllers, may necessitate modifications to accommodate it in most mainstream enclosures.
Plug & Play-ness. Are you a crafty or DIY-oriented person? If not you probably will want to choose one of the options that offer pre-built, or accessory kits like the MakersPEV flow-glider bundle for the foccer or the prebuilt funwheel controller box for the Thor 300