The one thing I wish more of these comparison tables had was licensing info, so for those like me who are curious:
1. GNU grep - GPLv3+
2. ack - Artistic License v2.0
3. ag (aka silver searcher) - Apache License 2.0
4. git-grep - GPlv2+/LGPLv2.1+
5. rg - MIT license
So with maybe the exception of rg, all are gpl compatible, that's great news.