Any user can create them. Before they existed, the forum was just flooded with affiliate links, which didn't give the customer anything, but paid the affiliate $97.
I'd say use one that belongs to someone that actually helped you out in some way, if you're not a customer and plan on signing up. If no one has been helpful, you can pretty much just pick one.
I believe 5050 is a current one that's direct from Dreamhost if you'd rather not give anyone credit for signing up.
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