Synthesis is in a category by itself when compared with the other tools. It has two specific areas where it is different – it’s designed by the people who brought you Genesis themes. And it focuses on content, SEO, and Social Media in a way that the other hosts simply don’t pay attention to. They also include Site Sensor, which notifies you if your site ever goes down. Additionally, they offer SSH for their Pro Plans and up.
This makes it hard to compare Synthesis, because while they do offer all of the above, they don’t offer staging areas, or an integrated CDN – something people get with other top of the line managed WordPress hosting plans.
If you prefer a more hands on approach and want SSH access, and don’t mind futzing around with CDN plugins to eek out a few more hundred milliseconds of speed, but do need to focus on your website content, then Synthesis might be the right choice for you.