One of the most important factors in my decision to move to SiteGround was on the personal recommendation of Brian Teeman (one of the co-founders of Joomla!) who spoke very highly of the Siteground team after his visit there in July 2012.
Also people like Nicholas K. Dionysopoulos from Akeeba Backup and Admin Tools and Anthony Olsen from JoomlaBamboo speak very highly of the service SiteGround offers.

SiteGround is one of - if not - the fastest Joomla hosting provider. Their servers are tuned to give your Joomla website the very best performance.
The above statistics show the performance of their servers vs others servers.
Joomla niche companies show results which were better than those of the majority of the general hosting providers. However, SiteGround have
achieved performance that is times better.
Each Joomla site installed by SiteGround has an in-built hackers protection against the most popular attacks. It is provided by their in-house developed Joomla extension jHackGuard. The extension is created and maintained by SiteGround senior support experts based on their years of experience in fixing hacked Joomla installations.
The accounts on SiteGround's servers are isolated from each other through a custom-made server setup, so even if there is one vulnerable installation, the other Joomla websites will be safe.
SiteGround closely monitors the general security status of Joomla and its popular plugins and apply strict security audit procedures to keep up with the high security standards. If major vulnerability appears SiteGround will apply server level security fixes often before the official development fixes are released.
The statistics speak for themselves: SiteGround's support is amazing!

You can save 60% off the cost of your hosting service when you signup here:
13 NoNumber Extensions
in the Joomla! Top 50
of more than 10 000 extensions