I ignorantly believe the demographic in my part of California doesn't really have an interest in things like this. It's just a matter of rolling the dice the morning of 3/26 in hopes that I've chosen the correct Target.
One thing is clear by the most recent Amazon pre-orders: Nintendo did not set a limitation as to how many can be sold to one customer. The merchant is apparently responsible for making that decision.
When I spoke to a Target employee, he said they prioritize online orders. So, even if you get to store at 6am, you could still come home empty handed if some random person/people decided to order all of the store's stock. It's best cover both; go to store early while keeping an eye on when the order is up and order as soon as you can whether it's for store pickup or delivery to your house.
You could also ask them a day or two before release to find out which store will get stock; I highly recommend doing that actually.