That would be MUCH nicer than Google buying them.
1) More investment from Amazon money wise than currently
2) Continued competition between Youtube and Twitch (or future competition).
Having two major services competing or being used is much better than one company having control over two big players. Plus Amazon is one of the few other relevant companies with the infrastructure already in place to grow/augment current systems that isn't Google.
Also beneficial for consoles, since Microsoft might not want to link up with Google-Twitch for live streaming for consoles as much as Amazon-Twitch, since Amazon and MS/Sony are more partners, while Google/MS are competitors. It keeps Twitch as something that is "compatible" with all ecosystems rather than potentially favouring one over the others or leading to conflict (for now at least).