Support, this is the most important thing about Interservers, their support is superb. I had several issues with my WordPress installation and database management, and they were quick to react. They have all types of customer service which includes an instant chat support that can be accessed right from your account dashboard. The payments are simple, they accept PayPal, which is absolutely huge for me and it's effortless to set up automatic payments via PayPal. Another thing is their pricing scheme, it's very straightforward and won't change over time like others. They also offer free domain registration with their domain service. When coming to the quality of their service, I only used their shared hosting plan and it's really fast for a shared service. You also have an option to get a dedicated IP address for a low price.

It's cheap, it's reliable, it's pretty easy to use, and the customer service was ok (but great for the price).

The best thing about InterServer maybe the performance of their server. I don't experience any downtime over the years of using it.