Today, Uptime Robot adds a new monitor type besides the http(s) and keyword checking: Ping.
It is actually the most basic command to find out if a network is up or down.
How does it differ from http(s)?
Http(s) monitoring sends a request to the web server and, in return, gets a status code from the server (like 200, 404, etc.). So, the server that the website hosted on can be up, other websites on it can be working but it may only be your website.
Ping looks for if the IP of your website is reachable or not. It is a better fit to monitor uptimes of servers/networks.
Should I use both http(s) and Ping for a website?
There is no need for that. If the aim is to monitor a website uptime, then http(s) monitoring should be enough as it'll notify you when the server can not be pinged as well.
However, if you have a dedicated server or a VPS, using Ping for the server IP besides the websites on that server is a good idea.
This is also an important step for Uptime Robot as how monitor types are handled both on the frontend and backend are now changed to let us adding new monitor types easier :).