RunCloud is made for web developers and businesses who just want to quickly setup and easily manage multiple WordPress pages or websites on cloud hosting using a web based control panel.
RunCloud provisions the server with the best tweaks and settings available, whether you are an administrator who do not like be bogged down with optimisation details or a user who might not have the advanced technical know-how.
Alternatively, RunCloud can also provide more control for advanced system admins or web developers who are more comfortable using the regular terminal commands to manage their pages or servers.
Plesk is mostly geared towards commercial shared web hosting as administrator and reseller accounts are easy to set up, including administrator accounts, email accounts, DNS entries and email servers, to name a few.
It comes with a lot of features better suited for resellers so you might be paying for features that you do not really need. Their monthly subscription starts at USD10 per month for up to 10 domains only.
Plesk does not have a free account tier.
Plesk has been around since 1999 with customers largely based in Europe so they have support in multiple languages in a few countries but since they offer a wide array of services that may interconnect with other services and features, your problem ticket might be escalated from one technical person to another, which is undesirable if you want a quick solution.
So RunCloud is perfect if you just want to look for a hassle-free server management panel to manage your PHP web apps on cloud and you do not need all the bells and whistles that a shared web hosting company offer. Besides, the support that you get from RunCloud comes from PHP developers themselves or who work closely with PHP.