Which Hair Color Developer Is Better?

Is it better to use a liquid developer or a cream developer to cover grey hair? Not so much in terms of application but, which one has the better results?

A liquid developer is an old version of a cream developer - they perform the same if it comes to helping color to be deposited inside the hair shaft.
However, supposedly a cream developer has better buffering qualities (what ever that means - I guess it may have something to do with conditioning the hair).
I would like to share my story. One day, when I was coloring one of my clients' hair, the salon run out of a developer and so I mixed a color of one company with a developer of another company - but the color turned out just very runny - dripping down my clients face. The color did not react with that developer as it should - it didn't thicken. My client's hair color came out beautiful, but the session was very "messy". Well not so messy, I had an assistant to stand by the client and wipe the dripping color for entire time.
Therefore, I truly believe that companies like to chemically "alter"  their hair color (and or developer) so hair colorists have to use THEIR developer as well.

So my advice - use a developer with color of the same company, if possible.