DNS has no effect on ping whatsoever. It is nonsense. DNS provides name resolution services and that is it. Nothing more and nothing less.
Your internet connection does not go through the DNS server, nor would routing through it improve your speed as chances are you will be going through several other connections (potentially on the wrong side of the world) before heading back to where you wanted to go. This does not happen normally anyway.
What Google or OpenDNS might provide you is a slightly faster resolution of names to IP address and possibly some level of protection from known malware domain names.
You might get a quicker initial name resolution, especially if your ISP has a small DNS cache and doesn't see requests for that site often, but after the first request both your server and local machine will cache the request meaning that Google or OpenDNS will be slower if there is a large distance between you and their servers. There will be no improvement to ping tests at all except for possibly the initial lookup.
I've said it in a comment above, but your tests are also not fair for the purposes of your testing. Using speedtest is not relevant for testing DNS and the tests you have run are resolving to different servers with different speeds or locations which will unfairly skew your results. If you want to prove that DNS makes no real difference then you need to be selecting the same server each time.
As to why DNS will make no real difference? It is because it is used in the first half-second of your connection to a server (to resolve a name to an address) and maybe if your cache times out then it will use it again. You might save a fragment of a second in getting the IP address of your game or Steam server, but after that the software will always be taking the direct route to the server and the speed will be the same regardless of DNS server used.
Having a fast DNS server can be good if you are browsing websites that are particularly laden with off-site resources such as social media buttons, advertising images and scripts and other resources which all need their locations resolved. This can be particularly annoying to most users as it appears to be the main site being slow when in reality it is the resolution and download of all the "extra" resources that makes the site slow.
Many people may equate this slow resolution of resources as being the sites "ping" being bad, when in all actuality the sites ping is perfectly fine. If the site loads faster with the DNS changed then it is your DNS server that is bad, not the sites speed or ping (latency). These are two very different things.
I've made a quick drawing of what (roughly) happens.
For existing connections and if the name is in your local cache you will see no benefit to changing your DNS. If the names are not in your cache then changing the DNS can make a brief improvement at the start of the connection.