Sara Tane's recipe shares that the best method to get the crispiest potatoes possible is to roast the potatoes before smashing them instead of boiling them.
This saves prep time and cleanup since you're already using a sheet pan for roasting to cook the potatoes with dry heat instead of waiting for them to boil in a pot.
Boiling the potatoes partially cooks their interiors and exteriors before roasting, which results in a creamier internal texture but a less crispy end product.
If you still prefer to boil the potatoes, let them steam-cool to release their excess moisture before smashing and roasting them. This will dry them out and crisp up the exteriors.
Although any variety will work, you'll want to find potatoes with plenty of potato starch for maximum crispiness, such as the Russet, Idaho, and Yukon Gold varieties.