Were on Unity, not that it matters really all engines nowadays are quite close to eachother.
Some excell at one thing, and suck at another.
Unity has it's plusses and minusses, in my opinion the best things are the compatibility, and ability to get things working fast. and plenty of build-in features plus the large asset database.
the downsides are it's performance and lack of a network engine.
Since we wrote our own network engine that is mitigated, and performance we are using many clever tricks to give the experience people desire.
In the end the engine is only a tool, it is what the game developers make of it.