It depends on the title. We won't really know for sure, though you can look to company history for a good idea. Bethesda has a strong PC presence at retail so I'd bet on it being a few DVDs to install rather than just a steam key. Though you might have to download a day 1 patch that's hefty anyway.
If the Steam Preload is up early enough you might be better off just getting it digitally since we won't know for sure until closer to release.
Thanks, bud. I appreciate it.