Marty McFly wrote: MXAO (as you maybe know) is based on Alchemy AO and therefore, along with HBAO+ and ASSAO which all work more or less the same, state of the art of 2012-2014.
[...]
Current state of the art method of computing SSAO is called Ground-Truth Ambient Occlusion, short GTAO. It's a fairly new method from Activision, which is considered an upgrade to HBAO and tries to estimate the occlusion as physically accurate as possible.
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Hope it clarified your doubts.
Besides, in that same post, Marty McFly announced an upgrade to his shader MXAO, based right on GTAO method.
If you're interested in that, you'll find it being included in the
qUINT collection.
Just change the preprocessor value "MXAO_HQ" from 0 to 1 to activate it, like this: