Just choose what you like! Isn’t that awesome? You can even buy a used board. It mainly depends on your riding style although there are 2 main things to take into account:
- board height
- board length
Height is important because all the electronics are usually attached below the board. If your board is low, the electronics might bump and scratch into things while riding, you might even get stuck on a bump. On “normal” boards, you can easily add pads between the board and the truck in order to increase the ride height if needed. Drop through longboards, however, will always be lower due to the way trucks are attached to the deck.
Length is also important because of the electronics. A shorter board just means you will have less space to setup the battery and electronic components.
In the end, again, it depends on your riding style, your esk8 use and how you want to setup the electronics. Try to get a rough idea of how you would assemble everything, and make sure it fits under the board. A lot of people use longboards because they offer a lot of space, good height and good stability (which is quite important when riding on a road at 30-40Km/h). But some people do convert penny boards to esk8 too.
A note about longboards: some are very flexy, some are very stiff. If you're not sure what to choose, you should probably test different decks before buying one. Flexy decks are good for riding & chilling. But if you want to go high speeds, stiff decks offer better stability.