Four questions get most people there.
How many people sit round it?
Diameter is the number that matters. 60cm seats four, 70cm five or six, 80cm six to eight, and the square bowls at 70x70cm sit five or six. Most people buy too big. A bigger bowl needs more wood before it looks like anything, and an 80cm Montana weighs 23.5kg empty.
Deep or shallow?
Shallow, like the Bali at 20cm, sits low, disappears when it's not lit, and puts the grate close to the embers. Deep, like the Haiti or Viking at 30cm to 50cm, holds more wood, keeps ash in on a windy night, and throws the heat outwards at the people rather than up at the sky.
If the fire's mainly for warmth, go deeper. If it's mainly for cooking, go shallower.
Bowl, basket or stove?
A bowl is the default: it heats, it cooks, it takes lids and grates and plates.
A basket burns upright, so the light sits higher and the fire shows through the sides. It's the one you buy for the look, and it won't take a grill plate.
A stove encloses the fire behind a chimney, pushes the heat forward at you, and keeps the sparks in. You can stand next to one in November. You can't sit around it the way you can an open bowl.
What will you add later?
The question people skip. Lids, grates and plates fit by diameter, not by model, so a 60cm bowl of any range takes 60cm accessories. Buy the bowl now and add the grate in July when someone suggests cooking.
Two exceptions: lids run slightly wider than the bowl and the pairing varies by range, so check the product page. And the Montana X uses a mast system with its own dedicated parts.