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Tesla should be doing your install if you placed your order for the Powerwall with them on the www.tesla.com site. You'll also find that they have the cheapest installation costs, since there's no 3rd party to mark up the Powerwall, the equipment needed for installation or the actual labor for the installation.
I went through SolarCity for my panels and powerwall. During the day of the install, SolarCity people did the panel install in the morning, then Tesla people did the powerwall install in the afternoon. Since SolarCity is part of Tesla now anyways it's all really just Tesla, but SolarCity people don't touch the battery in my experience.