You will remember from the Thumbnail Guide to the World Wide Interwebs that the internet is a giant city of trailer parks in the sky and your host is the specific trailer park where your website lives.
WHICH HOST
In the personal experience of Ofazomi, real satisfaction in the case of a massive web problems is pretty much non-existent across all vendors. Friends may be able to offer hosting suggestions. At minimum, your host should be running the most current PHP software and implement all patches within 24 hours. Other things to consider when selecting a host is their value proposition (cost/space), hosting options and back end administrative systems, but for most folks nearly any host should work equally well. With the notable exception of Laughing Squid, (please email if you know of others) nearly all tech support has been outsourced to India. Outsourcing tech support is not a problem until you want to speak with someone in management because everything has gone wrong. I have never spoken with anyone in tech support since the proto-internet days of the late 1980s is ‘authorized’ to offer their “guaranteed refunds.” There is no real accountability on the web. Pick your poison.
Can you be a bit more specific? I want to sell things online. (Click to find out!)