Rent-a-Wreck is the only company that does dockside pickups in Juneau - for the rest you have to take cabs to/from the airport. There is a lot to do in Juneau without a car, though. I've only rented a car once, to see the beaches up north of town - there just aren't that many miles of road. On some future trip I may rent again to do some abandoned-mine mine exploring...
Murray