Occlusion Master is great, but you use it on individual surfaces as opposed to on your overall lighting set up.

It's nice that way because then you have more control over what has AO and what doesn't, so you can save some render time by leaving out things that don't need the effect.

It's a great product and takes a lot of the guess work out of AO.  Over all, though it depends on how you work.  I don't use it with everything, a lot of time I use the lighting based AO settings instead.