Fast WordPress hosting means more than a fast server. Visitors need to find information fast, and that means a better search service than the default WordPress search.
WordPress Search Hosting
Rather than tweaking WordPress standard search with plugins, I prefer to replace it completely with a faster search engine
Google are the fastest, most comprehensive search service, and integration into your responsive theme is very easy.
There are several ways to do this, but unless you are using a theme that you have written yourself, you should make changes via a child theme.