We don't recommend that you bootstrap the Sia blockchain. While there are many trusted sources, the best source is one you don’t have to trust, Sia itself.
When you bootstrap, you're taking the consensus file from someone else who has already downloaded it (and potentially modified it) and using it for your Sia node. It's usually a lot faster than waiting for the Sia blockchain to sync, but that's the only benefit.
While there are a number of trusted community members offering the consensus file to bootstrap, you should let your Sia node sync the blockchain from the blockchain. Ironically, you should let your Sia node pull itself up by its own bootstraps.