AFAIK visual Quality from AO depends on implementation (hbao is better than standard ao) and also 3d model fidelity( more polys give better looks). Cheap versions can look dirty and cartoonish though.
I`ve seen BF`s HBAO and Watch Dog`s HBAO+.
They are quite nice. I`ve also heard of HDAO but I don`t know how that works!
Edit: After looking around for a little while, HBAO+ looks very nice! Twice the resolution of HBAO, half as framerate demanding as HBAO and much more acurate.